the e-recovery doesn’t package twrps openrecoveryscript - there you could issue twrp decrypt <pin> within adb… but can’t see the adb enable option in the twrp ui. The ui allows you to mount the userdata via UI though, right when you start it or later in its advanced menu.
fastboot boot twrp..img when you’re in fastboot
(I was curious how it works… code is at android_bootable_recovery/partitionmanager.cpp at 9d3ea68bc9e6687e94d2024d772736d80b33c4ef · omnirom/android_bootable_recovery · GitHub)