Since they have a /pricing page it would seem their business is not to make it easy to self-host but in fact to make people pay for the cloud version instead.
Mind, I don't think Plane's one of these. The open-source release seems comprehensive and the doc just seems not very good because the people who wrote it are experienced operators. But the claim being made isn't one that's easily put to rest except through the company in question committing to enthusiastic and comprehensive support that dispels doubts. (And, well--they chose that life!)