How to mount encrypted /data partition in recovery mode?

My current state:
Fairphone 3 with /e/OS installed is stuck in recovery mode, (I think) because there is not enough free memory space left. I need to erase some files from my Ubuntu 20.04 and I thought about using adb.

Problem:
I used disk encryption and now I don’t know how to access my data and where it is located. I can activate adb on my phone and access it from Ubuntu with adb shell command. For example if I run

adb shell

and then

FP3:/ # ls
acct        d              etc                    mnt                    plat_property_contexts     prop.default  sideload                  system_ext_property_contexts
apex        data           first_stage_ramdisk    odm                    postinstall                res           storage                   tmp
bin         data_mirror    init                   odm_file_contexts      proc                       root          sys                       vendor
bugreports  debug_ramdisk  init.recovery.qcom.rc  odm_property_contexts  product                    sbin          system                    vendor_file_contexts
cache       default.prop   linkerconfig           oem                    product_file_contexts      sdcard        system_ext                vendor_property_contexts
config      dev            metadata               plat_file_contexts     product_property_contexts  sepolicy      system_ext_file_contexts

When I then try to list the content of data/, storage or sdcard it shows an empty directory. How can I access my internal storage data?