I don’t particularly care about carrying over highlights from desktop to mobile but I do want the highlights to accumulate on the desktop-side over multiple passes.
The best I’ve gotten so far is using KOreader on mobile and Calibre with a suitable plugin on desktop, but that only exports highlights as text to the desktop without actually implementing them into the book.
I don’t read on my computer (running Linux) - but I do manage my e-books using Calibre… My e-reader is a Kobo - I’ve flashed it with an alternate version of the reader (can’t remember the name - it might be that one you mentioned “KOReader”?)… I can sideload DRM free copies of books (I mostly buy them - then grab a DRM free version) via USB between my e-reader and my computer (running Linux). Note - DRM content from Kobo is rubbish - e.g. if I increase the font size (which I have to do with EVERY e-book I buy from them) it increases the page count! e.g. I buy a book from their store, get it via wifi, open it, the font is tiny and unreadable to my 60 year old eyes, and it shows 400 pages, when I bump the font size up about 4 notches, I’ve suddenly got 2000 PAGES! WTF? That doesn’t happen with DRM free e-books! In fact with DRM free e-books - it REMEMBERS my font preferences from previous DRM free titles I’ve read!
But - I’m fed up of this… I’ve had more than one (like maybe 6) instances where the calibre database becomes corrupted (I can restore from Resilio Sync “snapshot” backup) - but that’s a PITA and doesn’t fill me with confidence. This corruption manifests itself by a number of titles showing something like “this entry has no content” (sorry - can’t remember the exact message - but basically - there’s a database entry, but no corresponding file in my calibre library folder on my $HOME).
Before I got the Kobo (Aura HD) in 2018, I used to use my ancient 3rd gen iPad, I’d “sideload” books this way :
Google’s ecosystem doesn’t particularly scare me either. I can manage my ebooks in a web browser window (on any computer) - and - if I want to read a bit of a book, on a computer, in a web browser, I can. Then open the same book in Google Books app on my iPad, and hey presto - it knows where I left off! Same with bookmarks (I don’t use them) and annotations…
After 4 years with the Kobo - I miss my old “workflow” such that I’ve ordered a 2nd hand iPad Mini 5th gen and intend going back to my old method. The iPad (3rd gen) was a bit cumbersome for casual reading (mostly in bed before I nod off) - but the form factor of the iPad mini is ideal (but a phone handset is TOO small for my comfort), and being 5th gen, it’s got all those snazzy features like turning off blue light etc… sure it will use more power, and won’t go nearly as long between charges - but - it’s also got multiple uses, i.e. it’s “almost” a computer - I can use my Pencil with it (I also have an iPad Pro 12.9 “2nd” gen - but that’s WAY too big for casual reading).
Here’s what I DETEST about my Kobo experience? Maps and images are nearly impossible to see - I can’t zoom in on them! Sometimes there are vital plot devices which are images, and I can’t view them on my Kobo! I have to unzip them (an epub is just a zipped up archive of HTML and content) on my computer then find the image files and view them on a computer - most UNSATISFACTORY!