I have a guess you are afraid because it has been so long since you have been alone with a man. It’s like anything else. The longer we stay away from something we’re nervous about, the bigger it becomes. Have you ever been in an uncomfortable silence with someone? The longer it goes, the harder it is to be the one to break it. It’s been 20 years since you’ve had a date. The rules have probably changed. The people you meet will most likely have been in relationships that for one reason or another didn’t work out. They’re nervous. You’re nervous. No wonder nothing happens.
The nice thing about an activity like volunteering is there generally are no expectations except to work hard at what you are doing. People get to know each other more gradually and casually. But fellow volunteers become friends only if you follow up by inviting folks to have coffee after the meeting or event or by taking other opportunities to get to know folks better (and to give them the chance to really get to know you). Focus first on making friends. Once you’ve got that down, the dating will probably evolve naturally.
You say you saw a therapist once. I’m very sorry the two of you didn’t talk through what was meant by “intimidating.” He or she may have meant nothing by it but you’ve remembered the comment and have felt bad about it ever since. I think it would be helpful to try therapy again to get some more complete feedback and because I do think a person with no friends needs some support as well as some practical advice for making changes.
I wish you well.