Christian McKee nailed the diagnosis - ALWAYS and ONLY the bottom bracket (removed, cleaned, lubed, and reinstalled).
Gratitude to everyone for their comments & support: seatpost & brakes are fine (Ryan Gwillim), chainring bolts were re-tightened while the crank was off (doug higley), spokes have always been solid on this wheel (Rayco, A Shopping Cart🛒of Bad Prose), pedals usually make a squeak not a creak when they're noisy (Harry Baggen). If this had been in a car, would have just turned up the volume on the radio (Doug Shanks 🏴󠁧󠁢󠁳󠁣󠁴󠁿 ) and, thankfully, my knees are still solid (Wake Gregg).
Dan Eller I'd define the "necessary maintenance" as the inevitable & seemingly frivolous rework one has to do not for proper function, but simply to help the bike understand that there's no need to complain so much or so loudly.
👋 Jason Plumb