Thanks @AnotherElk ! But I haven’t found yet this db file. Anyone else has experience with that? Or could anyone indicate me another forum about general Android issues where I could ask this question, which is not a purely FP issue?
You can do a twrp backup. This creates several extractable files.
It also creates the file recovery.log. There you can search for mmssms.db. In my case it’s at /data/user_de/0/com.android.providers.telephony/databases/
After extracting the compressed files you can find the database there. mmssms.db is an sqlite db. You can possibly later restore it or view the content via an sqlite viewer.