if the achievement works correctly, it is pretty straight foreward, just clear every level with 100% in the nature value.

The clearing doesen't have to be in order, so if you have finshed a previous level with less than 100% , you can return to it from the map, get 100% and it still counts.

You can actually overclear the asia/japan/panda-level (the one with the pandas).
In this level you will notice the nature completion reaching 100% despite there still being some dirt/ungrown plants.
If you want to get the perfectionist achievement, I'd advise to leave as soon as you hit 100%

If you continue cleaning, the internal nature counter can rise to a maximum of 102%, while your counter will still show 100%.
And the way the game sees it: 101 and 102 aren't 100, so you might lock yourself out of the achievement.

But if you're seeing this too late, don't worry. Later on in the last segment of this guide I'll show you a way to fix it and still get you that sweet sweet achievement.

In the africa-level some pieces of debris are stuck in the ground and under the camper.

This guide by para can help you get them.

This is where I myself was stuck for a bit. To my knowledge I cleared all levels perfectly, but the achievement just didn't pop.
Naturally in this position one would rather check which level one needs to redo instead of replaying the whole game.
The game itself doesen't let you check your progress, but there is still a way to see it.

Firstly you look for the games savedata on your device.

Ususally, you can find it here: C:\Users\*\AppData\LocalLow\Awaken Realms\Fresh Start
*your name
The "C" might need to be adjusted depending on where the game is saved.

There you'll find files containing the savedatas of your saveslots, e.g. if you only played on slot 1, you will find "slot_1.nplhsave" That's what we want to look inside of.

Just for safety create a backup in a different folder.

I opened the file by dragging it into an online save editor[www.saveeditonline.com]
since I didn't have a compatible program on my pc.

After openig the file, use the f3 key to search for "Nature". This will lead you to all the levels and their saved nature level.

e.g. \"railstation_Nature\",\"Value\":\"100\"

Now check every levels nature level to find out, which you need to replay. (note that the nature level of the tutorial is always "null", this is not a problem)

Sometimes, a level hasn't saved you completion properly (for me, alps was at a nature level of 4). In this case, just replay it to 100%.

Now there is also a bug in the Panda Level (Asia/Japan), that I adressed before.
You might have "Japan_Nature\",\"Value\":\"101\" or "Japan_Nature\",\"Value\":\"102\"
This will also prevent you from getting perfectionist.
But since we already are in a save editor, we can easily fix this problem by changing Japans nature level to a number below 100 (just using 100 would not work) , download the edited file, and use it to swap out the old file.

Now just replay the levels you need to replay, remember not to overclear Japan and enjoy your achievement.

Thank you to the people in this thread especially MntBerryCrunch who served as my primary source for this fix