I'm having the same problem as you. So I revert to a previous version (the 2018), as it accept the material updates I made (installing a new graphic card, and adding memory to my system).
The main problem comes from the software, as changing the properties of the folders won't change the saving problem.
3DS Max also ask for obsolete file format, when opening an older max file (from a previous version). But is does not save it, wherever you want to place the file.
It still accept the export way for saving files. So I'm trying to change the register association files, so that max files are open with the newer version of 3DS. But I don't expect much from it.
You can ask the maintenance service of Autodesk, and also try a new clean install (if you have time). I'm also trying a new complete reinstall of all of my system, on a new hard drive. I'll write about it in 1 or 2 weeks. It may run this way, installing 3DS Max2020 as the first external software on windows.