I can find no listing on Amazon re which Roku models Amazon has written their Prime Video Roku channel app to run on. However, Amazon announced in emails to Roku owners that, effective November 1, 2021, their Prime Video would no longer support the following older Roku model numbers:
Roku 2 HD/XD/XS models 2050X, 2500X, 2720X, 3000X, 3050X, 3100X
Roku LT models 2400X, 2450X, 2700X
Roku SE model 2710X
Roku Streaming Stick models 3400X, 3420X, 3500X
(The Xs or other letters at the end of the model number are distribution codes and are irrelevant for this issue.)
You can find your Roku model number via Roku menu path Settings / System / About
Roku Community Streaming Expert
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Streaming Stick 4K+ 3821 | Streaming Stick+ 3810 | TCL Roku TV 43S245/C107X