I know you said you’re biased against it, but TeamViewer is dead easy and completely free for noncommercial use. Sometimes the normie way is the best way, especially when it comes to the tech illiterate. Similarly, Chrome Remote Desktop looks very handholdy. I haven’t used it in many years, so I can’t personally recommend it, but I’ve heard good things.
You could also start a call on your preferred conferencing software, send them a link, and have them share their screen. Downside is you can’t control their computer directly. Zoom has a really cool annotation feature where you can draw on the sharer’s screen and they’re able to see it. I haven’t seen other conferencing software with that feature, but I haven’t looked very hard.