F2P Games and Software are displayed in the new Steam Library, even if they are no longer installed or available in the Steam Store. Also, check your Library page for Cakewalk to see if you had bought any Sound-Packs/DLC.

The only that comes to mind goes with Rythmik. Is that it?
(I truely am certain I have no other thing related to music creation apart that. Still puzzling to me. :S )

ADDENDUM
also seems not to be on my already bought list O.o

Rytmik is unrelated and by Cinemax, a different developer and publisher.

Cakewalk wasn't exclusively used for music. Although it did mostly give attention to musical elements, there were also sound-effect DLCs suited for video editors and game devs. This was apparently done in a small partnership with http://asoundeffect.com/ and featured sound designers like SoundBits and Diegetic Sound LLC and SoundFxWizard and Bottle Rocket FX and RDGSoundFX and TovuSound.

Remembering you from some other game-dev discussions, I was mostly saying to check if you had any of those before you do something like remove Cakewalk from your Steam account permanently. Even though Cakewalk is gone now, you would still be able to "install" it and get access to those DLC sound effects, if you had them from before (you can't buy them here anymore, obviously - though they are still being sold on ASFX independently if you search for those names I listed before). Without any of the DLC material though, Cakewalk Loop Manager is basically just an abandoned steamapp repository - and I'm not even sure if it installs executable software anymore (haven't checked in a long while).

The Cakewalk Loop Manager software itself was free (their model was to sell DLC) which means that Steam would have registered it to your account as F2P (free-to-play) and the recent Library changes enable Steam to display F2P steamapps even after they've been uninstalled (which is unlike the previous Steam Library). That's probably why you don't remember it and why it won't show up in your Steam Purchase History. You'll probably find it under License and Product Key Activation history, if you want to know the date when you first found it.

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If you want to know when and why it was de-listed from Steam, that can be found here https://gtm.steamproxy.vip/app/305280/discussions/0/2549465882933445833/#c1620599015901785410

The Cakewalk DAW (not the Loop Manager) is actually still around. It was acquired by Bandlab who is maintaining it and sharing it freely now (probably has a limited future for maintenance though). https://www.bandlab.com/products/cakewalk

Yeah I remember you from RPGMaker I think also... so... maybe a VX Ace or a MV thing/DLC...

Well. From there, maybe. We never know with those nwjs files that keeps popping up from games I run from those.

I'll try the history. (Still weirded out) Thanks for the hints. :3

It was promoted for free at one time, that's when I grabbed it.