It seems Google anaytics has retired the use of a Tracking code (UA-xxxx…) for integration and replaced it with a Measurement ID. And the Bubble Docs page needs revising?
In brief, where ever you use a UA code you can also use a GA4 code. Ie in your gtag.js library if you are embedding the code, or in any plug-in if you are doing that.
But as you note, Google will stop process UA requests in July 2023. I’m not even sure Google still issue UA measurement ids. I doubt it, GA4 has been around since 2019.