Thanks for the reply, as you mentioned "Please note that it is no longer possible to select the classic experience as the default for all sites in your organization." , I need to know-how for a random list in the site the setting looks like the following - and it definitely is classic?

I have the same issue on some of my sites

Thanks for your reply,
How can I check what`s the auto setting? I assume if I open a list or site content if it`s classic view means the default and automatic setting is "classic" right?

for instance, Before running the script, the site content experience was modern and we could switch

after running the script all has been switched back to classic

If I re-run the script-rather than deactivating the SharePoint Lists and Libraries experience feature- and use Auto rather than NewExperience do you know what might happen?
Thanks