The official suggestion (and what I use) is uBlock Origin in hard mode. It's not really matrix blocking but essentially does 90% of what umatrix did if not more.
https://github.com/gorhill/uBlock/wiki/Blocking-mode:-medium...
From there you can block 3rd party scripts and frames. To save the rule you need to commit it in the "My rules" pane by clicking on the temporary rule you added.