I agree. the Materialis theme is compatible with WordPress 5.6 and works just fine operationally and for development.
The problem is with Materials Pro 1.1.13 and Companion 1.3.14 and 1.3.18 on WordPress 5.6 hosted at Network Solutions and bluehost.
NetSol tried for a few days to get it running and surrendered when they could not provide PHP8 so I opened and account with bluehost who “thought” they had the then current (last Thursday) package operating properly. IT turns out that they only had the Materials version operating.
Step by step, we disabled all non essentials, downloaded a new Materialis Pro and installed it. Still only some pages would load the customizer and some edits did not stick when we moved on to another page. Note that the (broken) site renders perfectly but cannot be edited. The experience is that loader starts paints our site ghosted then just spins for hours on end.
Cleared cache, tried three browsers and tried all of that on three different PCs.
At this point, bluehost tech support cleared everything and started over then backed Material Pro back to 5.4 and all is good with PHP 7.4.13, M-Pro 1.1.13 and Companion 1.3.14 and auto-updates disabled.