What app do you use for reading ebooks on that one?

And how is boox. I've been looking for an ereader with a very big screen and haven't found a decent one yet, but the boox might be the one. Is the drawing any good?

I use the built in ereader software, called NeoReader. It's pretty fast, and after a small ramp-up of figuring out how to customize things (for instance, the font size wouldn't go small enough for me, so I had to learn that the "pinch-to-zoom" gesture could make the font size even smaller than the font size slider could go)... I've been really happy with it. I've also played around with KOReader, which works very well, too -- I'm just more used to NeoReader at this point, so I haven't switched over.

Drawing is very good in my experience, though I haven't tried the reMarkable or the Kobo Ellipsa. Maybe I just got used to it really quickly but it doesn't lag enough for me to actually notice when I'm writing on it, and hasn't slowed down at all since I got it.

I have an android ereader without a wacom layer, my favorite app to use is Moon+ Reader. If you have access to an android device, I strongly recommend trying it out. The customizations allowed are staggering and I can't imagine getting a new device that is unable to run it. KoReader is also great and open source. People don't love the way the animations work on an ereader but you could use the Kindle app as well.

How do you go by syncing your bookmarks with different devices?

Moon+ Reader has a built in cloud sync function and so does KoReader although I can't say more about KoReader as I only keep that installed on my old kobo.

Here's the link I followed to set up cloud sync for reading positions/notes/bookmarks:

https://raymondlamsk.blogspot.com/2018/03/moon-reader-how-to...

Calibre is a very useful piece of software regardless of what ereader you end up with, and there's this feature request about syncing back to calibre too but I haven't personally explored it. https://github.com/koreader/koreader/issues/3814

One annoying thing I sometimes run into is that if you keep wifi off, you'll have to remember to turn it to sync. But that's understandable.