It looks there are only 3 states that allow Driver’s License in Apple Wallet, at least there’s only 3 that show up for me when I try to add mine. Is it possible to use this feature with a Pennsylvania license?

FYI, your iPhone Wallet is only the “repository” of the Mobile Driver’s License.

All the “heavy lifting” needed to actually implement MobileID has to be undertaken - and supported by - the individual states.

A quick perusal of PA’s DMV website found no obvious mention of MobileID being under development.

https://www.dmv.pa.gov/

Not at this time. So far only 3 states have authorized it.