Migrate-NG is the open-source equivalent of Titanium Backup.

First create a backup. Flash the custom firmware. Then (unexpectedly) backup files! Yes, part of the restore process happens through TWRP recovery. Make sure you get rooted to the new firmware using Magisk.

Once everything is flashed, start the device. You'll get a notification to continue the restore process. Grant root access, relax, have a cup of tea, and wait for everything to recover.

The app is currently in beta and has some b