My Synology has an auto block feature that from my understanding is essentially fail2ban, what I don’t know is if such a feature works for all my exposed services but Synology’s

I’d be surprised if it works for custom services. Fail2ban has to know what’s running and haw to have access to its log file to know what is a failed authentication request. The best you can do without log access is to rate limit new tcp connections. But still you should know what’s the service behind because 5 new SSH sessions per minute and IP can be reasonable 5 new http1.0 connections likely cannot load a single html page.