In a way, TCP is just about as reliable as UDP, but at a different layer: TCP will either forward your entire stream of data in order and without gaps, or it won’t. UDP does the same, but on the per-datagram level.

Reliability is arguably more of a statement about the availability metrics of your underlying network; it doesn’t seem like a great summary for what TCP does. You can’t make an unreliable lower layer reliable with any protocol magic on top; you can just bundle the unreliability differently (e.g. by trading off an unreliability in delivery for an unreliability in timing).