Firefox's marketshare is small enough relative to Chrome's that some websites might just block it at this point, if Chrome users mean ad revenue and Firefox users don't.
It doesn't necessary cost a meaningful amount to a site to allow Firefox users to view it; it does however cost to make it compatible with non-chromium browsers. For most viewing that's a non issue (I mean, most crms are going to work) but specific sites might stop working (YouTube already got caught throttling firefox, and tbf, streaming would cost more than reading an article or something).
The numbers may be indicative of the general trend, but every single privacy oriented browser and so forth is spoofing the user agent, pretending to be the most widespread and popular os and browser.
Which is why privacy checks on my Linux+librewolf PC return win10 with chrome.
My worry is what the EU changes might mean for the mobile web and beyond. With iOS's market share and only the same rendering engine Apple used in Safari being available, sites/apps had to support more than just Chrome. If forcing iOS users to Chrome is an option (either through pointing them to the browser or an app built with that rendering engine), then there's even less of an incentive to test with anything else. It's great that users get more choice but if providers use it as an opportunity to reduce support for other browsers then it might not be a great benefit after all.