Safari "Reopen all windows from last session" functionality removed

Despite having this option checked in preferences Safari NEVER reopens all windows from last session and the option in History is greyed out. This question is often asked but generally ignored although I did earlier this year get one reply with some suggestions which didn't work. (Updating, restarting Safari in safe mode etc). I can't update OS beyond Big Sur 11.6.8 to Monterey due to the iMac being late 2014 model. Safari version is 15.6.

Has anyone found a work around other than ditching Safari?

Thanks!