Question I'm using Verizon 5g home internet. Currently not getting full 5G speed. Motherboard has built in WIFI 5 via m.2 module. Should I install a WIFI 6 mod

I can not be sure what you are talking about. Be nice if things only had one meaning.

Lately there are data cell plans they are calling "5g" this is something very different than the wifi band that for years has been called 5g. The wifi one actually means 5gigahertz but the cell plan one is just some marketing name. In addition this has nothing at all to do with
the so called wifi5 and wifi6. Just because all these things have a "5" in the name does not mean they are related.

You are going to have to be more clear what you are buying from verizon and what your problem is.