It's feasible: a couple of Lenovo Yoga Tabs do this* running Android 13+ until plugged in by an HDMI out (which I believe works with an adapter to USB-C).
Ex: https://www.lenovo.com/us/en/p/tablets/android-tablets/lenov...
*(Not touch-enabled in display mode, I believe.)
I have a Yoga Tab 13 (the more interesting sibling of the P-series) I regularly use as a standalone tablet and external laptop monitor - usually lives in the same bag. It's been perfectly seamless for me whether using a PC or a smartphone (surprisingly so). (I believe it shipped w Android 12.)
Of course, it's not epaper - but it is technically feasible.
I have a Yoga Tab 13 (the more interesting sibling of the P-series) I regularly use as a standalone tablet and external laptop monitor - usually lives in the same bag. It's been perfectly seamless for me whether using a PC or a smartphone (surprisingly so). (I believe it shipped w Android 12.)
Of course, it's not epaper - but it is technically feasible.