Recommendations?

Kobo, with either stock OS or KOReader (I use this, in part because the font size can be easily increased for my daughter who so far needs text larger than stock) or Plato.

Is the build quality and backlighting as good as the Kindle? And do they have a seamless option (no notched screen)?

I no longer have a Kindle to compare, but I'm very happy with build and lighting on my Kobo Libra 2. I've used Kindles since the Kindle 1, and there are some Kobo things that I don't like as well as Kindle, but it's a better-than-decent e-reader and I'm glad to be out from under Amazon's thumb.

I've been happy with the half dozen Kobos in my house.

Weirdly, about half of them have developed a problem after about 5-7 years, whereby they intermittently stop charging. Replacing the battery doesn't seem to fix it. Might be a problem with the soldering of the USB connector to the PCB?

As a bonus they are Linux based, and you can do fun things like replace internal SD cards with bigger ones, login using telnet and install new applications.

I imagine the Kobo is high on that list.

Onyx Boox. They run full Android, which means sync with Play Books, Kindle, Libby, etc.

A jailbroken kindle is okay - they make an adequate PDF reader and they can be found easily for less than the alternatives, at least in Britain. I do agree they're somewhat poor when used as intended.

They're also quite a nice embedded ARM Linux machine for a lot less than I could make one or buy one from elsewhere, but I suspect that isn't the core market for a kindle...

What’s the problem with the kindle? I use an old paperwhite and I have no issues reading epubs in it that I send by email