About point 3, just shoot on a Radioactive pool remove it. Shoot mode plus enable friendly fire allows it.

Not that I thought it logically, I was trying to use a Hydrazine can, put in the pool and shoot at it to explose and remove the pool. :-)

EDIT:
Shoot on it removes the Radioactive pool but replace it with fire. it's still can be useful. Some levels are flooded with water and in this case it just removes the Radioactive pool and can't fire the spot.

For non flooded levels, replace the radioactive pool with fire isn't a good bargain but such fire lasts only a few turns, so sometimes it can be handy anyway.

1) Turning off the power just makes it so the lights and doors don't operate. I haven't encountered a situation where I would want to shut down the power, but as you mentioned it will make aliens not attack the power plants.

2) Unpowered doors can't be closed. If the level has no power generation, or the generator gets destroyed, then they will be stuck if open.

3) seems like you already got the third point handled. I usually just jump over them though.

Originally posted by Ciecieji:

1) Turning off the power just makes it so the lights and doors don't operate. I haven't encountered a situation where I would want to shut down the power, but as you mentioned it will make aliens not attack the power plants.

Woo and I didn't noticed? Lol ok next time i'll check, but it looks weird and no reason to do it but in base defense.

Mmm perhaps make it explode can attrack aliens there during few turns, worth a try in a pertinent context.

Originally posted by Ciecieji:

2) Unpowered doors can't be closed. If the level has no power generation, or the generator gets destroyed, then they will be stuck if open.

There was always a working generator. And such levels always had some doors hard wired with security and working with control pad.

Perhaps try hack anyway the generator can allow re enable ability to close doors. But it would be weird as those levels start with a working generator.

In fact the general question is more how identify doors you can close to those you can't, I mean from distance. I added question 5 in OP.

Originally posted by Ciecieji:

3) seems like you already got the third point handled. I usually just jump over them though.

Yeah more or less as fire replace it, but there's use cases anyway.

Jump isn't always possible and it consumes more AP, when the whole team is involved it's impactful.

Eventually it's even more a matter of UI design, jump during move is cumbersome, it would be cool if the game allowed press a key so move path planed/shown/done include jumps, for the path visual its color could be a bit different and/or with stripes to hint there's jumps, and the jump could even been shown in the path visual.

Originally posted by Ciecieji:

1) Turning off the power just makes it so the lights and doors don't operate. I haven't encountered a situation where I would want to shut down the power, but as you mentioned it will make aliens not attack the power plants.

I had some opportunities to check turn off/on the power generator and for now didn't found more:
- Never had again those areas with all doors open and that can't be closed except those with a control pod linked, so could check yet if there was an opportunity to turn on the power generator. Weirdly in my new campaign (short, hard), Derelecit missions are quite different than in my 2 previous campaigns, perhaps a game change.
- Could turn off then on a power generator in space/ship area, and it's like you quote, it open all doors no sealed and doors can't be closed, turn it on enable again ability to close doors. I see zero useful usage of this feature.
- Could turn off then on a power generator in faction area that was flooded, same than for space/ship area case quoted above. And zero effect on water flooding the level. But I didn't let the power generator off during multiple turns but I doubt it would change anything just because there's not much logic unlike if it was to turn on from an off state. I quoted in encyclopedia a mention "valves" cluing the idea to close valves to stop water flood an area. But it's more a planed feature never implemented, it is quoted in section about hacking in list of interactions not requesting hacking, but it's not quoted in section about general interactions.

I tried once but could not explore much to try check a consequence.
About exploding a power generator, I ended quote that it didn't need create holes in the space ship/station, once it is blow up, cold start spread in the area like when there's holes in the hull.

Originally posted by Jarsonne:

Originally posted by Ciecieji:

3) seems like you already got the third point handled. I usually just jump over them though.

Yeah more or less as fire replace it, but there's use cases anyway.

I experimented quite a lot with that because I started use rather often Flamethrowers.

So shoot on hazard pool, creates a fire. And extinct fire is possible with:
- Shoot a weapon with cold shoot or cold ammo, the less expensive and a bit like an extra tool is use a dedicated Bulleteer with cold ammo.
- Push a create on the fire. For now it's 100% success for 100% types of crates that can be pushed. For sure for hydrazine barrel you'd better pick the barrel first. If the crate is on fire already it works anyway. In one bug cases probably created by alien garbage, you can have on same square hazard pool and fire, shoot on it removes the hazard pool, move a create on it as many time you want seems not remove the fire, but in fact it is removed but not visually. In this bug case auto path and move on it will identify fine the fire was removed thanks to the crate pushing. I didn't submit the bug yet, need check first if save and reload cancel it or not.

Originally posted by Jarsonne:

5. How identify visually doors that can be opened to those that can't?
Some cases are very clear:
- with destroyed elements,
- there's also case where the door rails is removed in half or fully,
- and I noticed recently cases with intermittent sparkles probably suggesting an electricity malfunctioning.

I found two ways:
- A hacking tools allow check it with 100% validity. And one hacking tool has a range of 10 (Primotron Chimeira), so you can see all doors that can be closed if they can be hacked. But also if they aren't in fog of war. To know if the game consider a door you see is still in fog of war, move the cursor above it, if there's no tooltip of door info on top, either it's a door broken either it is still in fog of war AND not in range of the hacking tool.
- Move the cursor above the door, if the tooltip on top shows door and armor values, then it can be closed. The if the tooltip isn't show it's either because the door is broken either because the game consider it still in FOW.

For now I never noticed counter cases.

Originally posted by Jarsonne:

...
4. Past interactions related to loot to pick + missions goals + doors + dig/break to open passages, is there more interactive elements than those?
....
- Any more? Any element has a name but sometimes I continue forgot check some types, for example, Fenced Artifact or Server Tower.

- Fenced Artifacts, there's multiple visual types but all with same label, armors and destroyed loot that is right like small crystal.
- Server Tower or Supply Pipe: Destroy one seems do nothing, I didn't bother try destroy all those in a level. Hack them or interact with them seems not possible.

I quoted that the encyclopedia (or perhaps the wiki) quote that most unattached elements fitting one square can be pushed, example quoted data bank. I didn't checked much this yet, there's already many cases of crates and shelves, but have the option of some more types can be useful.

I haven't yet updated OP with the new elements.