Could this Esim adapter from JMP somehow be used for the Librem 5?
On the face of it, it should work. You want to stump $50 to find out?
(It is my assumption that you would want the associated USB reader, rather than provisioning via an Android phone. With luck, with a USB-C to USB-A adapter and assuming that the associated USB reader is USB-A, you should be able to provision the eSIM adapter directly on the Librem 5 before powering off and moving the eSIM adapter from the USB reader into the SIM slot.)
See also:
Now out of testing phase and available for purchase: Newsletter: eSIM Adapter Launch! — JMP Blog
Also, the JMP people are very responsive in their official XMPP channel, so if you want any definite answers from them, I recommend joining and asking.
Yes, this has been my experience as well. Very responsive.