Some time ago I've built an OpenCV-based real time masks plugin for my videoconference tool but unfortunately had to limit it to a single thread WASM version because of browser support. That resulted in 320x240 videos when mask was on. However as an experiment I also ran a 8-threaded version locally and its performance on a laptop from 2015 was more than enough for an almost 30fps stream with a standard video size.
If anyone is interested you may check it out on https://xroom.app or even contribute with ideas and commits: https://github.com/punarinta/xroom-plugins/tree/master/nisdo.... For the masks I'd still recommend a desktop browser though.
If you're curious but don't want to bother clicking too much here's how it all looks like: https://imgur.com/93YR87e