I have setup so many instances over the months on different servers and the web ui always takes 40s to a minute to load per page I have always used redis for caching and the best methods even the aio docker image(s) are really slow.
kind of just been living with it for the past month or so but its really annoying when others are saying theirs takes seconds to load.
Nextcloud does need some tuning by default, specifically the php, nginx/apache, and database settings so that they all make use of more resources and some stuff like cache headers or opcode caching.
If you haven't used it yet, I think the AIO installation of nextcloud includes a lot of config optimization by default. I don't have experience with it, but probably worth a try?
I'm pretty sure the database tuning is what made the biggest difference to me.