You should make contact and give some simple small talk, perhaps initiating by sending a humorous video or picture if that's something you used to do, congratulate him on the engagement, make some small talk, don't pressure him for an invite and don't make it sound like you want one, do the congratulations in a very small passing moment, mid conversation just mention "oh congratulations on the engagement" see how he responds, after this talk or online chat, ignore him. If he makes contact, respond nicely and don't push the conversations, simple small replies, if he replies in detail or multiple times without you saying something, then he cares about the friendship, if not, then he doesn't.
If he doesn't message you in a month, then consider the friendship dead, don't bother messaging him, just put him in a restricted group in social media if possible, otherwise just remove him.
I have had friendships with people, pretty good ones, and then when I have changed location or got a girlfriend, just ended up dropping those friends. I've not wanted to carry them on when I am focusing on my girlfriend and my own life.
Likely thats what happened here, he is focused on his fiancee and doesn't think about you. As that is what it was like with me with my friends, soon as I got a girlfriend I just don't think about the friends anymore. There are some cringey messages from my old friends lying around where they have messaged me loads of times and I just ignored it when I saw them months later since I don't use facebook anymore, I have an account but it is mostly empty and has nothing important on it.
Personally I would suggest just removing him from all social media accounts, but it seems you want to carry on the friendship even in its current state, it will never be what it once was, he has other important things in his life now. So given you want to carry it on, do what I said at the top of this post and see how it goes.