Okay thanks! I executed the commands:
anonymous@anonymous:~$ adb shell
FP3:/ # ls /dev/block/bootdevice/by-name/userdata
/dev/block/bootdevice/by-name/userdata
FP3:/ # mkdir -p /mnt/userdata
FP3:/ # mount /dev/block/bootdevice/by-name/userdata /mnt/userdata/
FP3:/ # du -cs /mnt/userdata/* | sort -n | tail -n10
5132 /mnt/userdata/system_ce
17080 /mnt/userdata/misc
17336 /mnt/userdata/vendor
23048 /mnt/userdata/system
34888 /mnt/userdata/user_de
118424 /mnt/userdata/tombstones
3021288 /mnt/userdata/app
14200420 /mnt/userdata/data
32829028 /mnt/userdata/media
50273856 total
Also the other directories:
FP3:/ # ls -l mnt/userdata/ total 468
drwx------ 2 root root 4096 1970-01-02 14:24 adb
drwx------ 2 root root 4096 1970-01-02 14:24 adbroot
drwxrwxr-x 2 system system 4096 2022-11-11 15:41 anr
drwxr-xr-x 6 root system 4096 1970-04-28 05:40 apex
drwxrwx--x 56 system system 12288 2022-11-11 16:13 app
drwx------ 2 root root 4096 1970-01-02 14:24 app-asec
drwxrwx--x 2 system system 4096 1970-01-02 14:24 app-ephemeral
drwxrwx--x 2 system system 4096 1970-01-02 14:24 app-lib
drwxrwx--x 2 system system 4096 1970-01-02 14:24 app-private
drwxr-x--- 2 system system 4096 1970-01-02 14:24 app-staging
drwx------ 5 system system 4096 2022-11-13 13:22 backup
drwxr-xr-x 2 shell shell 4096 1970-01-02 14:24 bootchart
drwxrwx--- 5 system cache 4096 1970-01-02 14:24 cache
drwxrwx--x 4 root root 4096 1970-03-22 04:41 dalvik-cache
drwxrwx--x 297 system system 20480 2022-11-11 16:06 data
drwxrwx--x 2 system system 4096 1970-04-28 05:41 dpm
drwxrwx--- 3 drm drm 4096 2020-12-15 00:47 drm
drwxrwx--x 2 system system 4096 1970-01-02 14:24 fota
drwx------ 5 root root 4096 1970-04-28 05:41 gsi
drwxrwx--- 2 system wifi 4096 1970-01-02 14:24 hostapd
drwxrwx--x 2 system system 4096 1970-04-28 05:40 incremental
drwxrwx--- 2 system cache 4096 2022-11-05 16:04 lineageos_updates
drwxr-x--x 4 root root 4096 1970-01-02 14:24 local
drwxrwx--- 2 root root 16384 1970-01-02 14:24 lost+found
drwxrwx--- 3 media_rw media_rw 4096 2022-11-13 13:22 media
drwxrwx--- 2 mediadrm mediadrm 4096 1970-01-02 14:24 mediadrm
drwxrwx--t 55 system misc 4096 2022-11-07 12:22 misc
drwxrwx--t 3 system misc 4096 2020-12-15 00:47 misc_ce
drwxrwx--t 3 system misc 4096 1970-01-02 14:24 misc_de
drwxrwx--- 3 nfc nfc 4096 2020-12-15 00:47 nfc
drwxrwx--x 2 root root 4096 1970-03-22 04:41 ota
drwxrwx--- 2 system cache 4096 1970-01-02 14:24 ota_package
drwx------ 2 system system 4096 2022-11-13 13:22 per_boot
drwxrwxr-x 2 system system 4096 1970-01-02 14:24 preloads
drwx------ 2 root root 4096 2022-11-13 13:22 property
drwxrwx--x 2 system system 20480 2022-11-07 12:22 resource-cache
drwx------ 2 system system 4096 1970-01-02 14:24 rollback
drwx------ 2 system system 4096 1970-01-02 14:24 rollback-observer
drwxrwxr-x 2 system system 4096 1970-01-02 14:24 server_configurable_flags
drwxr-xr-x 2 system system 4096 1970-01-02 14:24 shared
drwx------ 2 system system 4096 1970-01-02 14:24 ss
drwxr-x--- 3 root shell 4096 1970-01-02 14:24 ssh
drwxrwxr-x 26 system system 4096 2022-11-13 13:22 system
drwxrwx--- 3 system system 4096 2020-12-15 00:47 system_ce
drwxrwx--- 3 system system 4096 2022-11-13 13:22 system_de
drwxrwx--x 2 system system 4096 2022-10-23 13:09 tombstones
drwx------ 3 root root 4096 1970-01-02 14:24 unencrypted
drwx--x--x 3 system system 4096 1970-04-28 05:40 user
drwx--x--x 3 system system 4096 1970-01-02 14:24 user_de
drwxrwx--x 40 root root 4096 1970-04-28 05:41 vendor
drwxrwx--x 3 root root 4096 2020-12-15 00:47 vendor_ce
drwxrwx--x 3 root root 4096 1970-01-02 14:24 vendor_de
and the question is now: Is there anything that I can remove more or less safely? I hoped to be able to remove data from certain apps. But I cannot find where the data belongs to.