There are numerous complaints in the Google Search Community Forums that the Google Search settings are not sticking. The most obvious example is when you have the dark theme set and Google toggles you to the light theme. But other settings are not sticking for some searchers as well, such as the region setting.
Google's Aishwarya Tapadar confirmed that the Google engineers are investigating the issue and hopefully will release a fix soon. Aishwarya responded to a number of complaints saying "Thanks for your feedback. We've asked our product team to take a look at this and we'll get back to you with more information as soon as we have it. Stay tuned!"
One searcher wrote "With new Chrome update when I want to search onto something and select "images" tab at the top google search always switching back into "device default" mode and the theme become light. (which I cant change into dark mode cause if I select dark mode here nothing happens). If I select any other tab and do a refresh everything is going back to normal. This is very frustrating, and started to happening only a few days ago since I've updated my Chrome browser. Any suggestions?"
Another person How do I put dark mode back, light mode hurts my eyes." Yes, Google is hurting people's eyes.
In any event, I assume this should be fixed soon and is only impacting a subset of searchers.