That's right, those of us who are immunosuppressed don't lead normal lives where we go to work, have DC in school, go to busy shopping centres, use public transport, go to gigs or festivals...
Of course we do, and we always did. We don't shut ourselves away and only did so when covid was an unknown entity, and there were no vaccines. Vaccines don't work very well for a lot of us anyway as our bodies are unable to produce a satisfactory immune response - they don't do much to stop us catching it, but they can reduce symptoms when we do. That's why I've had covid nine times and no, it's not because I go to loads of gigs and crowded bars or whatever (I've been to two gigs in three years).
All that said, nobody is testing anymore (well, the general population - I test weekly before I inject my meds, which is why I know how many times I've been infected. Some infections were asymptomatic and I wouldn't have known otherwise). I wouldn't expect anyone to not go to an event, particularly an outdoor one, if they had a cold or hayfever, which if you're not testing you would probably believe your symptoms to be.
Colds and flu kill immunosuppressed people all the time, and nobody expects people to stay home if they have a runny nose. Many people don't have that option anyway - they have no choice but to go to work or take DC to school or whatever. And I'm willing to bet that every single one of those telling you to stay at home and isolate have been to work with a cold in the past.
Ultimately it's up to you OP but if you decide to go, I hope you have a lovely time!