Downloaded the latest hotfix and it seems to have fixed the issue for me on Win10 PC. Previously the game would crash very shortly after pressing the Play button on the launcher, but now it launches and I was able to complete a mission without issue.
One user mentioned deleting/renaming the "steam_api64.dll" file that is located in the \Downloaded\Public\Tools\Windows\x64 directory, and I noticed after the update that file isn't even present. Perhaps it was placed there by mistake for the launcher version? Either way, game is working now and didn't need to download and install the Steam version and re-do all the custom settings I've set over the years, so I'm happy.