I’m a big fan of the Fellow Carter Move mugs. They definitely keep coffee hot (or cold) for quite some time. I actually have to cool off my freshly brewed coffee before I put it in the mug if I want to drink it in without waiting a long time. There are a few lid options, but I’ve found that the standard lid and slide lid keep temperature the best. There’s also several sizes available, though the 20oz is listed as a cold mug, it’ll work with the hot lids.

I realize I sound like a shill for the brand, but I just really like the mugs haha.

Looks like that is a home brew cap of some sort.