The RC-GZ1 remote is a recent Voice Remote issue that has no pairing button. They also have a tab you must pull out to engage the batteries.
To put these remotes into pairing mode after pulling the tab, press and hold both the BACK and HOME buttons near the top of the remote for 5 seconds or more.
Reference: https://support.roku.com/article/360011621473
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Ultra 4800 | Streaming Stick 4K+ 3821 | TCL Roku TV 43S245/C107X