Before to post this I was aware of my hosting resources and I believe that's ok(VPS with 30G ram and 8 cores). I will have a look into cdn plugin and webp optimisation plugin(cache I am using and indeed makes a difference)
It's not always about cores and RAM. When dealing with such software, the storage
I/O and latency is also hugely important, along with the software used for hosting (PHP version, Apache/LiteSpeed/Nginx etc.).
For example, LiteSpeed & Nginx are miles ahead of Apache, in terms of performance.
I remember back in the day, I had an extremely powerful VPS on Contabo, with the same specs as yours (30 GB RAM, 8 cores) but with a standard-bad HDD (no SSDs back then).
I can't describe how slow the performance was, the HDD being the bottleneck - and running on a VPS, that HDD was shared between a lot of users, so it stayed in 100% all the time (plus it was going bad I think). I had them change my VPS and the issue was solved.
Also, some software is more prone to DB queries (I/O operations) than others, and I think Osclass is one of them, as there were some old tickets regarding this, opened on the original dev repo (e.g.
https://github.com/osclass/Osclass/issues/2293).
That's why you might feel Flynax a bit snappier.
Test, test and test again.
Good luck!