Access to ADB in recovery mode TWRP – Samsung A3, Linux

I can access my Samsung A3 (a3xelte) in "normal" mode in linux using adb.
Today I installed the recovery mode TWRP 3.2.3-0 and entered it. According to https://www.droidwiki.org/wiki/TeamWin_Recovery_Project#ADB_im_Recovery, you should be able to use adb commands in this mode as well. However, "adb devices" does not show me anything. Is any idea or information incorrect for this phone?

Reason why I ask: after resetting the phone's factory settings, some valuable Memo-Notes seem to be deleted. I would like to copy an image of the partition to my computer (as described in https://stackoverflow.com/a/49287932/2135504) and then use testdisk to potentially find the relevant deleted file. The phone is not rooted, which seems to make things much more complicated …