This is a difficult one for me. My DDs are adopted and they already have a loving father in their lives, my DH. And also, as generally happens now, we do know who their birth parents are and can answer some of the questions our DDs might have. We also have 2 'later life letters' to read to them when they're ready to read to them, the first one for late primary and the second one for when they're teenagers. We read DD1 (now 10) hers a couple of years ago, and DD2 (7) is starting to wonder now, so we're considering whether this is the right time to read her first letter.
They may want to meet their birth parents when they're grown up; if they do we'll support them. We're in touch with their other birth siblings' adoptive parents and gave arranged meet ups in the past. So hopefully when they're old enough to use Social Media they'll be able to connect with each other, under our supervision.
My youngest DNephew is also adopted, with a loving father (my DBIL),but his birth father is unknown, as his birth mother refused to name him or even tell him she was pregnant. There's probably a very good reason why, as she also refused to involve her family at all, and his birth siblings don't even know he exists. So very likely he will do DNA research on websites like the OP did.
Sadly, he may well find that his birth mum had very good reason not to name him at all. My F sexually abused my DSis and me and some of our friends. The person whose DNA you have isn't necessarily someone you would want in your life. There are obviously some mums who are vindictive, but most women who don't reveal who the birth fathers are, or don't want them in their DCs' lives, have very good reasons for this.
And, also sadly, the majority of men who disappear from children's lives mostly don't have an interest in coming back into their lives to be a good dad and grandad. They might play lip service and talk about making amends, of course, and they might even think they mean it, but it's advisable not to expect too much.