As GP said, they have raised money before. So why are you now disappointed and think they "are selling out", when nothing has changed, and Tailscale has been a clear-cut for-profit startup from the start?
netbird looks like it would be a better option if open source is what youre after. theres a handful of others too, nebula, zerotier, netmaker just to name a few
that was disappointing
at least the current software is open source, so others can fork it before it closes down on itself and enshittifies.