Question marks appearing

I upgraded my iMac to Big Sur at the weekend and on the whole gone smoothly, I had been slow to do the change as I have my accounts programme which is still 32bit, I have got round that with installing Parallels and seems to be working fine.

But I have a problem with mostly emails coming in, they are HTML/rich text ones and some of the characters are showing as question marks, small screen shot enclosed. I have now had three long phone calls to Microsoft support and also two to Apple support and neither have been able to solve it yet – both almost saying it’s the other persons problem, we have done all the usual of uninstalling everything, including all preferences etc and that still did not fix it. If you forward one of these emails then the words show correctly in a font, but when it comes back in its wrong again. Tried a new identity and still wrong. The only time we have managed to make it work is when created a new user on the mac, installed my settings of the POP3 account and it displayed correctly. 

I still think it could be an issue with Helvetica Neue, but in Font Book it seems to be ok, it validates fine. Over the years being a service bureau I have had many copies of Helvetica and wonder if I have an old copy now installed. I have a MacBook Pro which also has the same issue. Today when talking to the Apple lady a page in Safari also displayed the same question marks, and also 1Password on the ‘date field’ shows question marks ! So it’s not just an Outlook issue, its in a few areas !

Any of you got any new good ideas please as its driving me mad with quite a few emails displaying wrongly, i have to click 'reply' to see what it says !