I always use OpenLiteSpeed on all servers, all is okay, 2,2GB ram max usage on 20! wordpress sites: https://prnt.sc/1qoeh5q
I must installed on 1 server (ARM Oracle) because OLS not support their REHL system. Nginx with 3 wordpress site eat 4,4GB ram: https://prnt.sc/1qoejyb
Newer db MariaDB is on Nginx, what I make bad? Why eat so much ram? Cleaning ram not help, on all WP sites are same security (Wordfence, All in one security, BBQ... etc), there no difference.
Only fresh new sites what 3-4 day started are on Nginx, so not much visiting 5-10 users daily.
How optimize memory usage? When I ad a few more sites, no ram available...