I’ve been using my selfhosted mailserver on a cheap VPS for a few years with no issues. It took about a week to get DMARC/DKIM/SPF setup right, and then a few back and forth email threads to my email addresses hosted on gmail, yahoo, and M365 allowed me to gain trustworthy status with them.
mind you, I’m the only user of my mailserver, so I’m not worried about other users spamming and getting me on a list.
I get what you’re saying, but I don’t think you’re going to find anything like that. Linux doesn’t really need some maintenance app running on top of it to keep it healthy. most of the programs that claim to do the same on windows,. android, etc. don’t really do anything helpful either. If you’ve got a specific issue that keeps popping up, perhaps we can solve it.
I don’t think you’re going to find a magic program that will just make your computer run faster. If there is a lot of CPU usage, something is using it. try to find out what that is, and either stop the process, wait for it to finish, etc.
if you have a lot of maintenance tasks that run and take up resources, maybe try and reschedule them for other times of the day?