Thank you very much for your time! 
Is it possible to remove some system files, like old OS versions or so? Not sure what parts are encrypted and what not. This is how the filesystem looks like:
FP3:/ # ls -l
total 1236
dr-xr-xr-x 4 root root 0 1970-01-02 04:54 acct
drwxr-xr-x 2 root root 40 1970-01-02 04:54 apex
lrwxrwxrwx 1 root root 11 1970-01-01 00:00 bin -> /system/bin
lrwxrwxrwx 1 root root 50 1970-01-01 00:00 bugreports -> /data/user_de/0/com.android.shell/files/bugreports
drwxr-xr-x 2 root root 0 1970-01-02 04:54 cache
drwxr-xr-x 5 root root 0 1970-01-01 00:00 config
lrwxrwxrwx 1 root root 17 1970-01-01 00:00 d -> /sys/kernel/debug
drwxr-xr-x 2 root root 0 1970-01-01 00:00 data
drwxr-xr-x 2 root root 0 1970-01-01 00:00 data_mirror
drwxr-xr-x 2 root root 0 1970-01-01 00:00 debug_ramdisk
lrwxrwxrwx 1 root root 12 1970-01-01 00:00 default.prop -> prop.default
drwxr-xr-x 11 root root 3580 1970-01-02 04:54 dev
lrwxrwxrwx 1 root root 11 1970-01-01 00:00 etc -> /system/etc
drwxr-xr-x 3 root root 0 1970-01-01 00:00 first_stage_ramdisk
lrwxrwxrwx 1 root root 16 1970-01-01 00:00 init -> /system/bin/init
-rwxr-x--- 1 root root 3171 1970-01-01 00:00 init.recovery.qcom.rc
drwxr-xr-x 2 root root 60 1970-01-02 04:54 linkerconfig
drwxr-xr-x 2 root root 0 1970-01-01 00:00 metadata
drwxrwxr-x 10 root system 200 1970-01-02 04:54 mnt
drwxr-xr-x 2 root root 0 1970-01-01 00:00 odm
-rw-r--r-- 1 root root 0 1970-01-01 00:00 odm_file_contexts
-rw-r--r-- 1 root root 0 1970-01-01 00:00 odm_property_contexts
drwxr-xr-x 2 root root 0 1970-01-01 00:00 oem
-rw-r--r-- 1 root root 36665 1970-01-01 00:00 plat_file_contexts
-rw-r--r-- 1 root root 48232 1970-01-01 00:00 plat_property_contexts
drwxr-xr-x 2 root root 0 1970-01-01 00:00 postinstall
dr-xr-xr-x 355 root root 0 1970-01-01 00:00 proc
lrwxrwxrwx 1 root root 15 1970-01-01 00:00 product -> /system/product
-rw-r--r-- 1 root root 107 1970-01-01 00:00 product_file_contexts
-rw-r--r-- 1 root root 3369 1970-01-01 00:00 product_property_contexts
-rw-r--r-- 1 root root 19971 1970-01-01 00:00 prop.default
drwxr-xr-x 3 root root 0 1970-01-01 00:00 res
drwx------ 2 root root 0 2022-10-28 15:17 root
lrwxrwxrwx 1 root root 11 1970-01-02 04:54 sbin -> /system/bin
drwxr-xr-x 2 root root 0 1970-01-01 00:00 sdcard
-rw-r--r-- 1 root root 1017092 1970-01-01 00:00 sepolicy
drwxr-xr-x 2 root root 0 1970-01-02 04:54 sideload
d---r-x--- 2 root sdcard_r 40 1970-01-02 04:54 storage
dr-xr-xr-x 12 root root 0 1970-01-02 04:54 sys
drwxr-xr-x 5 root root 0 1970-01-01 00:00 system
lrwxrwxrwx 1 root root 18 1970-01-01 00:00 system_ext -> /system/system_ext
-rw-r--r-- 1 root root 4382 1970-01-01 00:00 system_ext_file_contexts
-rw-r--r-- 1 root root 7036 1970-01-01 00:00 system_ext_property_contexts
drwxrwxr-x 2 root shell 100 1970-01-02 04:56 tmp
drwxr-xr-x 2 root root 0 1970-01-01 00:00 vendor
-rw-r--r-- 1 root root 80781 1970-01-01 00:00 vendor_file_contexts
-rw-r--r-- 1 root root 16818 1970-01-01 00:00 vendor_property_contexts
Strange how little memory everything takes. The 64GB should be full…