Multisite issue

Hello,
I updated my WP from 4.8 to 5.9 and after the update my multisite network stopped working.
When I go to Network Setup I see this error:

Warning: An existing WordPress network was detected.

All code from sections 1 and 2 already in my wp-config.php and .htaccess files

I only see my main wp site and no option to see other 2 sites that I have.
They were setup with subfolders.
I also enabled debug mode, but not sure where to look for more info.
Could you please help with resolving this issue?

Thanks a lot.

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