It seems recently that it can be a bit hit and miss using an internet browser when watching on a Mac or PC from the reports I have seen on the NOW Community forum and NOW Twitter (X).
I don't own a Mac myself, but have you tried any other internet browsers when attempting to watch NOW ?
I have a 2015 iMac, and it plays Now in Safari without any issues.
Sometimes, I wish it would break in the ways people describe, so I could dig into the issues further, but it never does 😢
As @schnapps suggests, try another browser. It has always been a problem with Now that the more you customise a browser, or even just use the thing, the more it is likely for Now to misbehave.
We’ve also had a couple of cases where the MacOS not being completely up to date has caused issues. And I have found that even with automatic updates On, that if I try updating manually, it finds something to do.
So before trying another browser, do a manual update check. If it does update, see if that clears the issue in the current browser, presumably Safari. If so, all well and good.
If not, try another browser. If it still doesn’t work, please report back.
If it does work though, I expect you’d still like to go back to Safari, as this scenario implies that the reason Safari won’t work for Now is that it is full of cruft, dead stuff like old cookies and data Safari has cached to save time in future accesses, but which is now preventing such accesses. Cached data can optimise processes, sure, but if the world has changed and the cache doesn’t know this, it can just send you down old paths that now lead nowhere.
So clear the cache, and to be sure, maybe the cookies and the history too. Things will be a little slower, perhaps, while the new optimised cache is built, but at least they will run.
Here’s how to clean up Safari:-
Good luck, and please let us know how it goes!