See also the changelog [1]. They've also added a free trial for paid plans [2]. Notably, new Personal accounts (formerly Free accounts) that use custom domains will be assumed to be commercial unless the user opts out of the free trial. This doesn't affect existing Free accounts [3].
[1] https://tailscale.com/changelog#2024-02-21-service
[2] https://tailscale.com/free-trial-offer-terms
[3] https://tailscale.com/pricing#i-am-a-user-with-a-custom-doma...