Thanks for the insights, confirming I had to pay for the bag on the LH operated flight (with Swiss codeshare) outbound, but didn’t pay for the checked bag on the UA operated return (with Swiss codeshare), my itinerary was booked and ticketed by Swiss, basic economy or economy light in LH’s lingo.

To the new question, it’s not clear but it sounds like Avianca ticketed your itinerary since they use this setup where their fare classes are basically tee shirt sizes. With UA silver you get nothing included on an Avianca XS (extra small) fare. You’ll check in with Avianca at the airport so wouldn’t be able to use any UA silver benefit unfortunately.

FWIW I travel to South America at least twice a year, Bogota, Lima, among other spots. Since Covid ended I avoid Avianca, the fare class structure by tee shirt sizes are a pain and the level of service is substandard imo. I far prefer Copa, flagship carrier of Panama and also part of Star alliance, with easy connections in a brand new terminal in Panama City.