Sorry about what comes next, but I'm really ****ed ...
After about three months nothing has changed.
I'm on Opera 118.0.5461.83 now an still each and every !"§$%&/()=?*# time I start Opera after hibernation or program exit I'm logged out of all sites.
No, I don't use third party or any cleaner at all and my cookies are set to stay.
That's not only annoying, it's a shame.
I've been using opera for more than 25 years now since v6 and after they dropped their own Presto Engine things only get worse.
Long story short, if there's no solution to this I'll drop Opera and switch to Vivaldi. I'm using it already as a second browser simultaneously.