The high beam don’t work. Fuses and bulbs are OK.
I’d suspect the switch itself on a car this old.
Use your 12V test light to check for power at the high beam connector(s)
I’m guessing you won’t find 12V there . . .
Are the connections good . . . or melted?
I’m mentioning this because we have tons of GM vehicles in our fleet, and melted headlight connectors are EXTREMELY common
I have seen a number of crispy connectors also in GM trucks, never had any Regals in the fleet, but certainly a consideration.