Fairphone | FP3+ | FP3 | previously on /e/OS 1.17-s-20231111351092-dev-FP3 | not rooted
All data seems to have been taken over, cannot find any data loss in phone app, calendar nor messages. 
Thank you folks!
FP3 upgrade from 1.17-S to 1.19.1-T
Went through /e/ recovery and used ADB sideload to install the upgrade from the computer. (Eventually) Used the download link @AnotherElk suggested (direct download shortcut to save you having to sort out the back slashes size: 1.1 GB). Took just a single-digit number of minutes to install. A bit doubtful at the end when the FP3 recovery display’s bottom line just read (step) “2/2” and no (further) confirmation that install was completed. Just went back to the recovery home screen and rebooted into system, and there it was booting into Android 13. 
P.S.: Unfortunately the Recovery still would not offer me any option other than installing through ADB Sideload. No SD card option (although portable storage SD card is in the device) shown, neither internal storage.