Should I avoid confined spaces when dh now has serious heart functioning failure?

I would not go. It is too easy to catch or carry any one of these winter infections from being in a closed space with other people in a small room. They may not even know if they are brewing something or may not feel ill enough to stay away. All too easy to pick up these bugs and pass onto vulnerable people and it is so very hard for that person to shake the infection off once it is in them and it causes an awful lot of suffering and anxiety. Tbh you can wash your hands and sanitize them till the cows come home but you have to breathe in and out around 10 times or so every single minute but most of these infections are airborne so clean hands will not help. Another few weeks and there will be fewer bugs circulating and you can open windows during your craft group. I would be very hurt if my husband decided meeting his friends was more important than my health.

Mu husband is immuno optimised following a kidney transplant bit we decided together that whilst we would be sensible so far as not mixing with family/friends who are known to be ill , we coukd as easily pick up something from a stranger in a supermarket so we chose to risk living our lives as normally as possible.
You need to make a joint decision and then, ask the other people in the group if they are or have been unwell. They will understand.

Compromised not optimised!!!

I went to the hairdressers a day after hairdresser came back from a cruise. She was sounding sniffy and a bit bunged up. I made sure not to touch my face and went straight home to give my hands a good wash.

I was meant to be going to craft group two days later, I decided not to go, the risk was far too great for the other 12 people, who are generally older and some are frail. I wanted to protect them, just in case

Most people just go out and about, harboring the nasty viruses which are rampant this winter so yes avoid confined spaces where viruses are easily airborne