how can i remove a game completely off my account

[sprinbluch]

including achievements and all that type of stuff

[Seretti]

Build a time machine to go back and not buy it?

[J4MESOX4D]

You can remove a game via the Support wizard but it only acts as an advanced hide and it can be restored at any time. Things such as achievements and time played will remain.

[cSg|mc-Hotsauce]

Originally posted by sprinbluch:

including achievements and all that type of stuff

The permanently remove function through support is an advanced hide function that can be restored at any time and no stats are removed.

https://steamcommunity.com/sharedfiles/filedetails/?id=1636709697

[Nx Machina]

You cannot remove achievements, playtime etc because that is part of your gaming history, in the same you cannog do that on any other PC platform, nor consoles.

[Glimmer]

While not a removal, the new Private feature will achieve some of what you want.
https://help.steampowered.com/en/faqs/view/1150-C06F-4D62-4966

I think it's currently only in the Beta branch, so you'll need to switch to that if you want to give it a shot.