It sounds like you are doing this to solve a Permissions issue.
How about if when the Table B Record is Saved, you trigger an Automation to Copy the lookup field into a scalar mirror field.
But then as you point out, you need that scalar field updated if it�s lookup value changes due to an Edit if the Parent record. You can also use an Automation to trigger a saved table to table import, merging Table B into itself and mapping the lookup field into the scalar field. The saved table to table import will be filtered where the lookup field is not equal to the scalar field.