I was having the same issue after installing the patch but on Epic, as were/are many other people on the steam forums, reddit, twitter etc, so it definitely busted something with the launcher.
If you go into the game properties in steam and add “-skip_launcher” to the launch options (without the quote marks) it should then start fine.
The same solution works on Epic; click the three dots on the game icon, select ‘Manage’, then ‘Launch Options’ and enter the -skip_launcher command.
Hope this works for you!