This is part of the solution. Here is what worked for me on Windows 10 (PC)
As suggested in the earlier reply, Go to Settings / Apps/
You will not see a choice for optional features anymore, so type it into the search bar
It should display the optional features you have installed. You need to add Internet Explorer 11, so click "+Add". Microsoft will not offer you Internet Explorer as an option, so type it into the search bar. Click it and it will add it to the optional features. This will allow QB to open.
If you want the updates to work, you need to take one more step. Go back to the start menu. You will not see Internet Explorer (even though you just installed it.) Type it into the search bar. Microsoft really does not want you to use it, so they will open a couple of windows of Edge on top of the IE window. Take your time and close them. When you get to IE go to the settings/ options / security. Select the "Sites" tab. Scroll down to the checkbox that requires only one site at a time (specific http:// address). UNcheck it. Go back up to the dialogue box and enter two lines:
*.quickbooks.com
*.intuit.com
save and now you are really finished and back to QB functionality. It is working fine with my QB2020. Am now moving my instance of QB2019, but do not anticipate any problems
