you can preload them as I understand.

one of the major apps for doing that is openeuicc: https://gitea.angry.im/PeterCxy/OpenEUICC

if you look it won’t work on unrooted phones, but it’s easyeuicc variant can still be used in the stated ways.

f-droid also has the jmp sim manager: https://f-droid.org/packages/chat.jmp.simmanager its a fork of the former, but it works 100% in unrooted phones with the jmp esim adapter that you can order in the app