I believe this is a major bug as of Nop v4.50.2
It appears that without a lot of work the "CustomProperties" of various models (i.e. Store, Customer, etc.) do not work by themselves.
1. The first problem I ran into is that when a form is posted back to a controller, those custom properties are not processed and do not exist on the model. Despite verifying that these values are posted in the POST DATA, the ModelBinder does not process those values.
I was able to fix this issue by following these instructions, although they are a little outdated:
https://www.nopcommerce.com/en/boards/topic/89966/modelbinder-problem-for-basenopmodelcustomproperties-object-dictionary
2. The second issue is that none of the "nop-editor" or "lablel asp-for" tags will work with these custom properties. So far I have not solved this problem. The only way I've been able to utilize the CustomProperties is by manually writing all the HTML code for these pages.
Ideally there is a solution, but if not, this needs to be addressed in an upcoming version of Nop. I would think it would be easy to implement fixes for both of these but as a rule, we don't like to modify the Nop core code.