I want to buy the Roku express 4k+ and to know how to avoid buying an older version ie 2021 model!
Always check the model number and avoid any listing that says "Latest version" or gives a year and not a model number.
You can find the latest versions of all models here:
Roku Players | Roku
It appears as of 11/26/22 the latest model is 3941R2. The suffix after the 4 digit model number is usually superfluous and model numbers that only differ in the last digit are most likely identical other than included accessories.