I know that, thing I am asking is do they have a limit of many people in England can access 4K feed. On bbc iPlayer there’s a limit and then once it’s full you can only watch in HD.
The BBC did state
We're also excited to announce that both the UEFA Men's Euro 2020 and Wimbledon 2021 will have UHD coverage as part of our trial!
I did experience 2 incidence of the UHD stream not being available on Iplayer over the past month with a message to try again later. On the first incident i was able to access at half time . on the second occasion i tried and suceeded after a few minutes.