It’s an A11 design, not really a bug, though it does bug some people.
There is already a feature request via the FP3 beta world to bring back a simple ‘switch’ select 2.4 or 5
However I suppose that given I can select which I want at home by using dif SSIDs maybe it’s not going to present a problem when I am out as by design A11 should pick up the best signal. I.e it will select 5Ghz if available 2.4Ghz if not.
And presumably if the 5GHz signal is weak it will switch to 2.4Ghz
However having the option to decide would be more comforting to me.
As the FP3 has just been updated to Android 11 the same issue has now arrived there, as mentioned.