G'day roni-Opo, Welcome to Linux.org
There appears to be some confusion here
You have said that you are running Linux Mint 21.....correct?
You are not running Impish 21.10 .....correct ?
Why exactly impish was showing in your LM21 sources list is a bit of a mystery......
You have to delete it, both because mixed-version repositories are bound for disaster, and because impish is EOL and the repo's been removed.
You have already removed it......so that can only be a good thing.
Give us a little more detail?.....did you only recently install LM21 ?....how long ago?....where did you download it from ?
How did you install it?
Do you know how impish repository get on to LM21 ?....do you have any idea ?
By the way you did not do anything 'stupid'.....there is no such thing here....just learning experiences.