I think that's a self-fulfilling prophecy. Sure, it's more difficult to make friends when we are older because as children we are a lot more accepting and don't care as much about diverging interests.

MeetUp groups have converted to online meetups. Bumble is a service for making friends - it's an app that has a function for dating or for friendships. You could use it for making friends who you have the same interests with. There are even subreddits for your favorite TV shows and you can communicate with people through social media who share similar interests. It's very possible to make new friends as an adult, I have had to do this myself, especially after the turmoil I've been through. In the last 3 years I've drawn a core group of good friends around me who I didn't even know existed three years ago. The friendships started off slow with one or two shared interests and over time we became closer.

It's uncomfortable to go through the process of making new friends, and it can be slow, which makes it more uncomfortable, I don't deny that. But if you can acknowledge that it won't be done tomorrow, and will take time, and be patient, in a year you may find yourself with a solid handful of friends that you trust and value.