"I have good bulbs"

Are you sure? Can you test each bulb by, say, cutting the outlet off an extension cord and touching the now-exposed wires to the bulb contacts?

Thank you for responding!

I need to report that I found the issue. I un-installed everything down to the wire nuts, then checked all wire nut connections. The ground and power/black were fine. However, when I applied a bit of pressure to untwist the wire nut on the common/white, I felt the Romex 14 gauge wire break and separate.

I strongly suspect that the elderly wire cracked when I first applied the wire nut to twist the Romex wire to the light fixture braided wire. With the crack, there may have been enough connection to pass voltage with no amperage load, and therefore test adequate in a no-load test. But when I put the bulbs in the circuit, the demand of load was too much and failed to pass amperage through the cracked wire.

I refit the wire ends of both wires, then replaced the wire nut with a WAGO push-in connector. I re=assembled everything, turned on the power circuit, and viola! The lights now work fine.

Final thought . . . anytime there is a need to connect a braided wire to a single Romex wire, it might be wise to just use the WAGO connectors rather than wire nuts.