As a hobbyist, this bums me out; I no longer will have the data from the day my humble blog made the front page of HN. Wish there was a way to migrate UA data to GA4, but from a bit of digging that doesn't seem possible.
Keep in mind Google can suspend and lock your account at anytime for "suspicous behavour", there's no one you can contact, use this shutdown of UA to make the change today and start owning your own data. There are plenty of other good alternatives in the other comments.
That’s the price you pay for not owning your data.
Same. I run a hobby site, and like being able to look back over all time and see the (in my case slow and gradual) buildup of traffic. The lack of migration route for historical data is frustrating, but I also don't particularly appreciate extra non-value-adding work being dumped on me for something I do for fun.
Its possible to export a reasonable amount of current googld analytics data via the api.