What model and model number is your Roku? Settings > System > About will show you, or if you can't access the Roku home screen, look for a label on the device.
Some lower end Roku models only support the 2.4 GHz wifi band. If your mobile hotspot is set to use the 5 GHz band, try setting it to 2.4 GHz.
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. If this post solves your problem please help others find this answer by clicking "Accept as Solution.".
Streaming Stick 4K+ 3821 | Streaming Stick+ 3810 | TCL Roku TV 43S245/C107X