To sum up, a reasonable flag combination can be as simple as -Xmx4G -Xms1G -XX:SoftMaxHeapSize=3G -XX:+UnlockExperimentalVMOptions -XX:+UseZGC. That is it. There are bits that you can squeeze from complicated flags, but you would get much more from modified server software. In fact, all serious discussions (e.g. Aikar and brucethemoose) of server performance assume some degree of modding.