Funny story…
After I got it running again (by replacing it with the old stable version) I got me the following plugin (this is no advertisement, just what I did):
https://de.www.ads-software.com/plugins/wp-rollback/
Unfortunately I am using the wordpress.com site autoupdate service.
So I ran into the same problem again. As I still had the backend open, I could use the WP-Rollback plugin and it worked again (for me, just reporting here).
But sadly, I can not disable it for w3tc anymore within WordPress.com. When I try to disable it for w3tc it sneakily just updates it again. And after that I am not even able to list the plugins anymore within WordPress.com, as it gives me an error.
I tried other ways to disable updates, which unfortunately didn’t work:
https://www.wpbeginner.com/wp-tutorials/how-to-disable-automatic-updates-in-wordpress/
I was trying the following approach:
add_filter( ‘auto_update_plugin’, ‘__return_false’ );
So what did work this time: In the backend of my website (not WordPress.com), I:
* rolled back to 9.4.1
* disabled the plugin.
Now I logged into the WordPress.com backend and:
* disabled auto update for w3tc
By the time I reached the option, it had it updated to 0.9.5 already. But this time, it didn’t break the website.
Next step:
In the backend of my website I:
* Rolled back to 0.9.4.1 again.
* Activated the plugin.
Logged into WordPress.com:
* Checked the plugin state, and IT WORKED. No automatic update anymore.
Finally, using the private surfing function of my browser.
IT STILL WORKS!
Closing Time!
Finally leaving work for today, happily