To add on here, this is how I've been able to do it

I started contributing to OSS in highschool, worked in closed source to get by, kept up contributions, eventually got hired by Citus through an HN Who's Hiring right when they got acquired by MS

After a year of working on OSS Citus extension I was moved to managed service. I continued to contribute to OSS by day tho as I would try upstreaming changes / fixes

At PeerDB (now ClickHouse) I'm again in OSS, & continue to contribute to other OSS projects as part of my day job. I'm fortunate to be working in a culture that respects devoting working hours to OSS. That's not really a coincidence when I've been doing OSS on the side for years beforehand

This isn't for everyone: I spend hours programming outside work, & I agree it's unfair to expect everyone to devote their off hours to programming. But that's how it happened for me