I noticed your post with a startup settings screenshot on Mastodon. I just checked the system settings on a Fairphone 5 running the standard Fairphone OS, and it seems to me that what you are shown on the startup settings is just a selection of 5-6 (probably) most common English variations. Once you are in the actual system settings later, you can customize your English language setting to a(nother) specific country.
While I cannot check this on an FP5 running /e/OS, I also checked it on my personal FP3 running /e/OS and it’s the same.