Many of the recently introduced and more popular channel apps were not written to be compatible with older units that do not have the more advanced capabilities of more recent models. And many channels that have been around for years have dropped support for older modeks. The more different models you must support the more complex the app must be and the myriad of combinations that must be checked when updating the software increases exponentially. Some channel apps will still run on your HD but an increasing number will not.
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