Apologies for leading you in the wrong direction with this answer originally.
After installing nvm again in a test WSL session (I usually use n myself) I see that Linux nvm is installed as a bash function, not as a binary. This means that whereis nvm doesn't actually see it, since whereis only looks for files.
> type nvm | head -1
nvm is a function
Two things to note:
When entered without a fully-qualified path (absolute or relative), the function will take precedence over a binary. So as long as type nvm returns the function, you should be fine.
And the fact that you mention (in the comments) that your path starts with /home/seefer/.nvm/versions/node/v14.18.0/bin means that the Linux nvm is working correctly and prepending the correctly activate directory to your path.
If you are experiencing issues with node or npm after using the nvm use or nvm install commands, let us know.
While whereis nvm finds /mnt/c/Users/seefe/AppData/Roaming/nvm/nvm.exe, you would have to actually run nvm.exe for it to run the Windows version.
There is one more thing to watch out for here, though, that is related to that other answer.
npm on Windows is a strange one, since it actually does ship with a shell script (even though it is for Windows) named npm that in turn calls the Windows npm.exe. If you have Windows Node/NPM installed (and it sounds like you do), be careful that you always active the Linux version (so that it is prepended to the path) with the Linux nvm.
Otherwise you can get into issues with Windows npm trying to run under WSL/Linux.
Be careful with this. As long as you have activated a node/npm installation with the Linux