The Sopranica/JMP wiki provides this simple CLI guide for using a Linux computer with an eSIM reader to manage (i.e. view, write, rename, enable, disable, or delete) downloaded eSIMs on an eSIM adapter (i.e. a writable SIM card):
eSIM Adapter/lpac - Soprani.ca Wiki
Then you’ll be able to use the written “eSIM card,” with the desired eSIM enabled, in the Librem 5 as normal.
An eSIM adapter will have enough space to write approximately 6 to 8 eSIMs, but in Librem 5 v.1 you won’t be able to manage them from the SIM card slot. However, @jcs has stated that v.2 is hoping to implement native eSIM support.