FSF somehow got my real name ;-)
I just opened the latest newsletter from FSF and in the text I saw my *real* name and surname, instead the usual phrase "Dear Free Software Supporter".
I never gave them money, sign any petitions, also I never used my identity data on mailbox settings, both at the mail provider and on Thunderbird SMTP settings.
All this seems both curious and also a bit concerning?
Not at all. You gave it to them at some point. Ask them where/how/etc. They don't go data mining; I'm sure they'll be happy to say how it happened. None of us will ever be able to do anything more than speculate, which is probably not helpful.
> I'm sure they'll be happy to say how it happened.
It is not really a matter of whether they are happy or said. Every data controller has certain GDPR obligations and the data subject has certain rights. No controller can process personal data without the agreement of the data subject.
The fact that perhaps only 0.1% of controllers are truly GDPR compliant is another matter... But still the OP has rights.