I carried out a quick online search, which suggested a fix for the problem by disabling
OCSP through the about:config
settings area in Firefox. This is not an ideal solution
as it reduces the security of the browser.
How to diagnose connection problems furtherWith all Power Apps problems that are related to connectivity and
authentication, the first thing to try is to use a different browser. Alternatively, we can clear cookies/browsing
history, or try the in-private/incognito modes of the browser.
I tried again with Microsoft Edge and the cause of the problem became very clear - the time on the computer was incorrect.
Your clock is behind Can't establish a private connection to http://make.powerapps.com because your computer's date and time (Friday, 18 February 2022 at 07:07:48) are incorrect.
a series of power outages that were caused by severe storms in the UK,
the computer I was using had lost its time setting, and was several days behind. Once I corrected the time, I was able to use Power Apps without any further problems.