I'm not the OP but also have a reMarkable 2: the reMarkable 2 doesn't appear to mount as a standard USB external disc on MacOS (Kindles do, however). This makes it hard to manage a library via Calibre or a similar system. The reMarkalbe 2 really, really wants users to sign up for subscription services that manage the device through reMarkable's servers, which adds a bunch of unpleasant and difficult-to-manage steps, relative to the simple strategy of "plug in, send to device" that Calibre enables.

In addition, I often download articles from https://www.instapaper.com/u; the reMarkable 2 often malforms them, in ways other e-readers, including Kindles and iPads, don't.

I infer that reMarkable's scheme and hope is to sell monthly sync software, but this plan works poorly with my e-reader workflow and, I'd guess, others'.

Probably there are ways to get around these limitations (and, reading the thread, I see some people listing rsync and such), but they're so annoying out of the box that I wish I'd not bought mine.