Restore Catalina TM Backup to Mojave


Hello all

I took up the task of reverting a relative’s MacBook updated to Catalina a month ago back to Mojave. The Mac never had a Time Machine backup taken on Mojave. What I did so far:
1. Partitioned an empty 1 TB disk to 2 macOS extended partitions
2. Took a TM backup of current instance of Mac on Catalina on 1 partition, created bootable installer of Mojave on 2nd partition
3. Booted from bootable installer, erased internal disk and installed Mojave on the internal disk
4. Booted on Mojave and tried restoring from Migration Assistant which supposedly restores only the files and not the macOS

Probably due to the new way things work on Catalina with Macintosh HD split to system and Macintosh HD - data, macOS Mojave only finds 1.4MB of data to restore which brings back nothing essentially. I think the issue lies with Mojave not understanding how the Catalina structure works and tries to restore files from the Macintosh HD folder that contains no user data whereas it should be looking to the Macintosh HD - Data folder. I can potentially hand it over and have my relative set it up all over again (install apps, login mail and Apple accounts) and then bring over manually files to the ~/Library folder to have the app settings back, but I was looking for a workaround to restore the Catalina user files back into Mojave that potentially will save some work (although I’m sure that will create issues on some apps upgraded for Catalina use). Would that be possible?

I created a clone of the TM backup from Catalina in order to safely play around with it but macOS is not allowing to play around with contents of dated folders, even when the disk is a clone and not directly linked with Time Machine. Is there a workaround to that? I was looking on deleting the system “Macintosh HD” folder from all dated folders of the backup and renaming “Macintosh HD - Data” to “Macintosh HD” on all folders and attempting a data migration from Migration Assistant after. Would you think that would work?

Thanks in advance to anyone that will help on this.