When this thread was going I would have passed with nothing to say. (Little did I know.) I took a 23andMe test early in the year, mainly interested in the national origin part of it. What came back in that regard was not surprising, but the DNA matches were.
My sister was not my sister, but was half-sister. I also had a half-brother and another half-sister, plus a 1st cousin with the same surname as the new half-sister. There were a couple of known names on my Mom's side, but none on my Dad's. Within a week, I had a message from a 2nd cousin 1R saying that she had sperm donors in her family, and from the half-brother saying that I was the first half-sibling to show up and that he knew his paternity was from a fertility clinic (that happened to be within an hour's drive of where I grew up).
I replied that it didn't seem right to me, and I pretty much mentally shelved the whole thing as covid provided lots of distraction. From time to time, I would get an Email from 23 with a list of new matches (as more people took tests). In October, I sent out some more reply messages to the earlier contacts, and also asked my sister to send me a look at her Dad side of the family tree from 23. Her Dad side did not match him either, and also did not match mine. I pretty much accepted at this point that my Dad was not my bio-Dad.
I then got more replies from the DNA relatives. It turned out the 2nd cousin lived about an hour away from me, and we exchanged phone #'s. She was well informed about the donor and the family, except that the donor wanted to remain anonymous, and was disturbed that DNA testing made it a risk of being found. She shared some family info, trying not to to get too close to the donor. I was able though, to take what I learned and figure out who it was. I also heard back from the new 1st cousin and half-sister, and we have had a phone and a Zoom call. I've talked with the half-brother too. I expect that when covid is managed, we will get together at some point.
In November, I took an Ancestry test to see if there were different matches there, and mid-Dec. I found out that there were. So far though, none of them have replied to me. Some may be unaccepting, as I was at first, and some may be donor relatives and also want to stay private.
Both of my parents have passed, so I have no one to ask about this.
I took a dive into the ancestry of the new paternal line. In addition to filling out the information that I had "lost", I discovered that both of my Dad's were descended from the same person who came to New Jersey from Scotland in 1685. It rather helped to learn that.