I think it worse than that. I don’t think Donny has had any real or close friends for most of his adult life stemming from his childhood relationships with others.

He seems to be distrustful of anyone and can only see them for their value to his goals. Once they stop being useful or compliant, he gets rid of them or distances from them. Look at Musk, seemed real close and Donny manipulated Musk’s autistic nature as a useful tool, only to cut him loose once Musk realized the reality and wasn’t on-board anymore.

His marriages may be evidence to support this as well. Melania was around 28 and working as a model, which is “too old” for that line of work, and she saw him as a viable means to keep her dwindling career alive. She eventually latches into him because of his connections and wealth. She was a model to hang on his arm and tolerant of his cheating enough to stick around because she had aged out of being a model and didn’t like other prospects. I suspect their marriage is open as a convenience and to avoid a divorce that would no end well for Melania and/or Trump. A marriage that is more a business partnership than a relationship of genuine love, as if Donny is even capable of genuine love.

He probably grew up with others like him, who learned from their parents, that people are only useful to have around until they aren’t. This mirrors business relationships. Allowing for personal relationships opens you up to weakness and leverage over you, which can’t be allowed if you are to be successful.

The business world probably reinforced his view of personal relationships. People you would consider friends may end up getting in the way of your next step, so you have to position yourself emotionally so you can cut their throat and not think twice. You may do things to better your situation that may screw over a friend directly or indirectly, can’t let your feelings get in the way of doing what must be done for your interests, if they won’t capitulate.

Epstein was probably very useful for whatever purpose he served to Donny due to the known connections Epstein had, but problematic enough to keep a distance from. So he got a birthday card, just to keep enough of a connection should his utility become needed. I think he knew what Epstein was up to very well, but probably didn’t partake because he was/is too distrustful of anyone to allow them to get such leverage over him.

If he has/had interests in Epstein’s products, it is more Donny’s style to use a power imbalance to get what he wanted; like getting the daughter of an illegal immigrant or a beauty pageant contestant(maybe via the overbearing mother of one living vicariously). Having Epstein arrange for something would expose Donny to manipulation and I think he would not allow for such a degree of trust in another person.

So yeah, I don’t think he was friends with Epstein because he isn’t friends with or close to anyone.