I went through the same and found friends in what are (for me) unusual ways, so I think I can help, here are some tips/ways/ideas to make friends as an adult:
1. Dating apps: they aren't supposed to be used for friendships, but weirdly I made a bunch of friends through them. I don't know your gender and I admit it might only worked bc I'm a woman, but it's worth a try.
2. Waiting rooms: when your doctor keeps you waiting, don't only look at your phone, try to talk to someone. I made a friend like that, so it has my "proof seal" too.
3. Online communities: have you though about having long distance friends? I had them when I was a teenager and never thought I would come back to it, but now I have an amazing friendship with someone and I love it!!. I know it's not "ideal", you can't go to events/places together (or often) and talk face to face, but they can be a good companionship. Also, I would say you can dm me but I still can't receive messages :(
4. Old friends: Sometimes we lost touch with someone cause of distance or routine, but can be great to send them a message, see how they're doing and maybe schedule a date, you never know. Plus: if you guys were friends once, you already like each other. Social media is great for that! Post and react more to stories, iniciate a conversation based on their post, etc.
5. Other friends - get togethers: this mainly depends if you already have friends, of course. But if you do, invite them to events and tell them to bring one or two more friends, that way you'll get to know more people. Same goes to be present at any events they may throw.
6. Other "friends" - parties: a party can be an amazing place to make new friends, even if you don't know anyone and went by yourself. If you're extroverted, be yourself, enjoy the party, engage and talk to people, after a bit of time you'll be talking and exchange social media! If you're introverted, alcohol can help. But it's important to emphasize that I said "other friends" because you'll probably start to talk to one person and they'll introduce you to their friends.
7. Friendship apps: ok, you tried bumble, but there's a bunch of others apps. Remember that you won't be friends with everyone and some people won't like you as well as you won't like some other people, etc, but you shouldn't give up only because it didn't work out with one person. I was ghosted several times and still made friends.
Know that is common not to have many or any friends in our age, a lot of people are struggling with that and looking for friends too, so don't give up, your people are out there. Don't put too much expectation on it, just live your life and be open to the possibilities. Also, keep in mind it's not supposed to be hard, but to happen naturally, probably when you least expect it.
And I'm very shy and made friends in all of these situations (tips) mentioned, so you can do it too!!
Some other things I was told that are great to make friends but I never tried: courses in general (can be just for fun, like pottery), going out by yourself (they say people just approach you) and virtual groups from your city (can be found on social media or dating apps but I don't recommend).
Hope it helps, good luck <3