Once I graduated from school, I found it hard to make friends. My mid-20s were very lonely when I moved for work.

A few things I did:

I periodically had roommates. This wasn't the same experience as a college roommate, but at the time it helped with the loneliness.

I started going to tech meetups. (I lived in Silicon Valley.) This ultimately was where I met most of my friends.

(When I worked from home,) I would occasionally work out of a hacker space. After I changed jobs, I remained a member and went to social events. This was where I met the rest of my friends.

I volunteered.

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Some things that didn't work for me, but might work for you:

I tried going to church. (In my case I found a hippy interfaith that focused on world religions instead of Christianity.) This didn't last very long for me for reasons that I won't discuss here; but if you find a community that you like, it can work wonders. Churches are fundamentally social organizations.

I went to Burning Man twice. The community operates similar to a church. For various reasons, it didn't work for me, but if you're on the same wavelength of a Burning Man or "local burn" group, it can work for you.

I would often sit at the bar for 1-2 hours in the afternoon and have 1-2 beers. Sometimes I had great conversations, but it never lead to friendship.