I suggest to start with fresh Volumio installations on both devices. Install Touch Display plugin version 3.4.0.
On the Pi 5 add
dtoverlay=vc4-kms-dsi-waveshare-panel,11_9_inch
to “/boot/userconfig.txt” (assuming the display is connected to DSI1).
On the Pi 4 add
dtoverlay=vc4-kms-v3d
dtoverlay=vc4-kms-dsi-waveshare-panel,7_9_inch
to “/boot/userconfig.txt”.
In case you want to rotate the displays try the option on the Touch Display plugin’s config page.