hi my friend ,So I try your files. There is my result.
On V6.3 via TWRP,
I install the file 01_Gallery_Settings_MyFiles and I restart. No problem et nothing change. I switch off my phone and restart on TWRP.
I install the file 02_OneUI_IncallUI_Messages and I restart. The theme change ok and no problem..
I switch off and restart on TWRP. I install the file 03_Dialer_Contatcts_TelephonyUI. I restart, the theme change and ok.
I switch off and restart on TWRP. Crash of TWRP (language choice) Restart TWRP and I install the file 04_SecureFolder_DeviceCare_ThemeStore.
I restart my phone but he stay on Bootloop and don't start.
I restart on TWRP and restore my full backup. No problems. I re install file 02 and 03.. Everything OK. Theme change and no crash.
I dont know what file are problem. Maybe 01 or 04, because TWRP crash before i intsall 04 !!!
well ... i think the problem is Device Care app ... this new full theme is without it ... try it when you can
don't uninstall the updating of Device Care app anymore