I move back and forth between the standards. My laptop and 75% mechanical are ANSI, my work laptop and Bluetooth keyboard are ISO.

You’d be surprised how quickly you get used to switching between them.

I had the exact same question a couple of years ago. I was a very long time UK ISO user, and then some of the keycaps on my keyboard broke. When looking at a replacement I fancied a mechanical DIY, so I bought a Glorious Gaming GMMK TKL, still UK ISO. But the selection of keycaps was small, even with UK sellers, e.g., on Etsy. So, I got an ANSI version of the same GMMK keyboard, and some nice blue & white keycaps from an Etsy UK based seller.

It took me a few weeks to get used to the layout. The Enter key is not a problem, it is things like @ and # not being where your muscle memory expects them. Also, the lack of a £ key. Because, being ANSI, you need to use the US keyboard layout in Windows, which does not have £ or €. Eventually I used the Microsoft keyboard layout generator to create a custom layout, with £ mapped to function 3. I think I mapped € too.

I can share my keyboard layout file if anyone wants it.

I am too stuck in my ways. On an ANSI board half the time I hit the return in the wrong place.

I largely use HHKB layout keyboards and although this doesn’t really answer your question, moving from ISO to HHKB took me about 2 weeks to fully adjust. I still miss having the £ key though, so for any non-HHKB layout keyboards I still actively look at ISO if I can. I’ll say that if you use an Apple keyboard (MacBook etc) you’ll find they’re already about halfway between ISO and ANSI (@ above 2, " above ’ etc) which can give you some idea. At this point I can use ISO, HHKB or an Apple keyboard and I won’t have to think about it at all really, I’ll just naturally adapt to the layout.