Emails are deleting on their own (not in trash or spam)
 

So I managed to find some of the emails but it’s like half of them have been deleted, and it wasn’t by me, it’s not in The trash or spam folder. Is there a way I can recover them? Then I also have the spam folder marking legitimate emails as spam which has led me to no choice other than just accepting all email and having to manually mark them as spam, which defeats the whole purpose of a spam filter.

Well some email services delete mail from known bad sources, before any filters or spam engines do their processing, so one never actually receives them. Maybe that's the case here.

The thing is that half my emails are gone, I doubt that would be possible. Especially since it’s been forever now I know it’s too late. There’s nothing I can do to get them back?

See if your email provider has backups??

Was there a "first half" to this discussion that's gone missing?

I mean, where is the info like

- who the mail provider is
- whether a webmail system, or mail client is being used
- if webmail, which browser & and are any ad/script blockers in use
- if client which version on what OS; any antimalware system in use
- whether it ever worked properly/as expected
- when it started going wrong

Google mail? They don't, they have a email recovery form but I did that and they have a stupid service for recovering deleted emails.
I went everywhere else, I have no way of getting them back because when I singed in on my computer I was using the browser and it wiped some of my emails.

Google mail, and Yahoo mail
I used no client, it was in a browser
I had no extensions or ad blockers
This was on Windows Vista (Which means it had to be an bug or malware)
There was no unexpected behavior, everything worked normal, the only difference is that I can't find certain emails, and they are not in the trash or spam folder.
This has happened once in 2018 but now it happened again this year

Also I don't know if this is new or related but my email filter has been altered, where legitimate emails are marked as spam automatically, I tried to revert the settings but google still marks regular email as spam. This makes it more difficult because I have to unmark everything as spam and manually mark "spam" as spam and it defeats the whole purpose.

Sounds a bit like a scammer tinkering with your messages i.e. deleting them to hide their activity.

Have you reset the passwords on the accounts and checked the security/recovery settings (e.g. phone number, recovery email)?

If your messages in GMail have been archived without a label, you can try this filter ...

None of that works, it's as if the emails have been deleted, and are not in trash. I'll just mark this as resolved, there is nothing I can do to get them back.

Another possibility could be if you allowed a program or other account access to your accounts via POP and did not select the "leave on server" option.