Some channel providers have a "one login" feature that will log you in automatically on other Rokus linked to the same Roku account. Most do not -- on those you'll need to log in on each unit.
By the time you get to the 4th TV, you'll be really good at it. 😉
Roku Community Streaming Expert
I am not a Roku employee, only a user like you. Please, no support questions via private message -- post them publicly to the Community where others may benefit as well.
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Ultra 4800 | Streaming Stick 4K+ 3821 | TCL Roku TV 43S245/C107X