So what you've leaked is the information that you have an interest in private conversations. This might be a problem in some countries, but I think it's fair to ask folks in affluent countries with working (sorta) democracies to shoulder that burden. I.e. you don't donate if there's elevated threat to your safety, there are enough people who aren't under elevated threat.
There's also the possibility of using a donation mixer like Silent Donor, though I'd evaluate that very carefully. (There's a record of the transfer in, and the mixer needs to keep temporary records for transferring out. There's also the question how you verify the mixer doesn't skim.)
Some donation mixers accept crypto currency, so for maximum paranoia, I suppose crypto->crypto mixer->donation mixer->charity might be workable. Or hand cash to a friend who donates in your stead.
As always, the best path is to set aside paranoia and build a threat model instead to see what the actual risks are.