I shelved ideas until I had a cofounder.
I shelved other ideas until I had a cofounder and capital.
Other ideas I built myself.
I’ve met like minded people that also had the right risk profile typically at mixers and tech meetups on topics that I liked. Never for the explicit purpose of meeting a cofounder. Just people that happened to be in the same fireside chat as me that contributed good conversation. Its all luck but you can improve the odds.