Coming from the old Bulletin Boards (BBS) era and then from standalone PHP forums, i was happily surprised when i found wpForo for WordPress forum plugin, a few years back.
While a plugin for WordPress and while is has WordPress limitations, wpForo is very close to a real standalone forum script. wpForo has a huge amount of features, it is completely free and if you need some extras, you can buy some plugins at a very reasonable cost.
How about speed? wpForo has its own db tables within WordPress database and doesn’t use custom posts. That removes some WordPress limitations but still wpForo does a lot of database transactions. Especially when you have a busy forum. But despite that, the speed is adequate even under a shared hosting plan, due to wpForo efficient internal caching. If you run (or plan to do so) a big forum with lots of traffic, you will need a powerful and stable hosting plan.
How about SEO? wpForo has its own SEO support, so make sure it is fully compatible with your SEO plugin. Some SEO plugins are “wpForo aware” but not all.
How about Optimizers? wpForo is already internally optimized. But works right with Autoptimize plugin, if you need it. Still in 2022 and http/2, page optimizers are useless IMHO.
What makes wpForo to really stand out from other plugins, is the exceptional support for a free plugin. gVectors run a busy forum for wpForo, with plenty of information and fast support from staff that knows what they we talking about.
If you need a Forum plugin for WordPress, wpForo is the definitive plugin for you.
You can check some useful information for wpForo:
Also you may check some high quality and reasonably priced plugins for wpForo.