>multitasking for a long time is not a free lunch

The multitasking I was talking about was combining a mindless repetitive task that has low cognitive demands such as walking on a treadmill, yardwork raking leaves, driving on non-descript boring roads ... with listening to a podcast about whatever topics are interesting. The mind is engaged while the hands and feet doing the work are on autopilot. In those cases, it can be a "free lunch" in the sense that the curiosity-seeking mind got fed while whatever physical task that needed to get done also got done with less procrastination and dread.

I wasn't talking about trying to edit a Excel spreadsheet while listening and concentrating on a podcast about the politics and protests of datacenter buildouts.

Yes, or the question is how much of both are you really engaged with and will remember at all. And then if you do, maybe the information was crap and not worthy of your attention anyway. I think anything really worth doing is worth doing at your 100%.

With the right kind of music, it's not multitasking. A soothing repetitive beat with no lyrics (lofi or trance for me) is perfect for me to work with, without getting an overwhelming sensation.