gsdsam
If you’re on linux you can use id3tool
I did this a while ago for incorrect tags on my Plex and it worked well.
https://manpages.ubuntu.com/manpages/lunar/en/man1/id3tool.1.html
If I understand correctly you would just need to put all of the files you want into one folder, navigate to the folder in your command line and then run id3tool -G Jazz *.mp3.
It operates off a list of predetermined genres which you can identify by running id3tool -l
Furthermore the *.mp3 will apply it to only mp3 files, if you have other formats and would like to capture all files simply remove make it just * instead.
Sorry I can’t be more specific as I can’t fully remember, but I thought I’d comment in case it helps.
For downloading a bunch of music, especially more obscure stuff, soulseek might be worth a try - if you search a genre you like you can then explore the libraries of the posters - some are very extensive. Just make sure you follow whatever guidelines they set out on their profile before you download a bunch of stuff, definitely make sure you’re sharing some music yourself on the platform and that your listening port is set up otherwise you might get blocked.
So what I have been doing on pen and paper (that I want to turn digital) is noting what I have done morning, afternoon and evening and my mood at each time out of 10. It’s not super complicated I guess. Although I don’t use it for the same purpose, I think the technique is called behavioural activation.
The reason an an app called daylio (not OSS) was recommended to me is because it also scheduled push notifications to submit entries at those times. With just a calendar event, I will get distracted and end up neglecting it, because even though the steps are simple, tapping to fill it in right away increases the chance instead of navigating.
Other than that key aspect yeah I’d say some kind of spreadsheet/CSV format could work well.