Glad to see this thread revived; I'm Irish and so always seeking potato perfection.
Lately I have been cooking "baked" russet potatoes in the Instant Pot: 14 minutes (so much more convenient than 60 minutes in the oven), then natural release (although I suppose you can force-release earlier if you want to). Come out nice and hot and fluffy, skin dry but not necessarily crispy; if you want that, you can put them in a hot oven for a few (5-10) minutes afterward.
I bought some sweet potatoes for Thanksgiving planning to steam them in the IP as well. I haven't yet looked up how many minutes it will take, but I expect it to be more than the 14 min for russets, given the size and density of sweet potatoes.
As to what to add to potatoes you intend to mash, I love all of the dairy addition suggestions (milk, buttermilk, cream, sour cream, cream cheese, butter), but what I've also heard, and what has worked out well for me, is that BUTTER should be the first addition, because it melts and coats the starch granules and prevents them gumming up. After that, you're free to add whatever creamy and/or other additions you like for purposes of flavor and fluidity. Curious to know what others think.
Finally, it may be that cooked potatoes are not as delightful to eat when reheated as when freshly cooked, but I've read some things that suggest they're actually better for you: cooked/cooled/reheated potato becomes a resistant starch that functions much like fiber in your digestive system and in that sense is healthier for you than fresh cooked potato. Same is apparently true of rice, and, unless I remember incorrectly, bread. Curious to know what others have read about this.
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