You can have, I believe, up to 20 Rokus linked to a single Roku account.
Some channels to which you subscribe may place limitations on how many simultaneous streams of their content you can have -- most all allow at least two.
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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Streaming Stick 4K+ 3821 | Streaming Stick+ 3810 | TCL Roku TV 43S245/C107X