Issue with internal storage in Catalina

I’m currently running Catalina 10.15.7. I understand Catalina splits the internal storage into two separate, but linked volumes - a ‘read only’ volume for system files and a write volume for applications and user files.

On my desktop I have ‘Macintosh HD’ and below it ‘Macintosh HD - Data’. From what I’ve read I should only have one icon showing and it should be called ‘Macintosh HD’.

Now in ‘Disk Utility’ under ‘Internal’ I have three volumes listed:

‘Macintosh HD’ with it’s icon showing a small insert Finder icon (read only)
‘Macintosh HD’ with it’s icon showing a small insert house icon (writable)
‘Macintosh HD - Data’ with just the plain HD icon (writable)

Again from what I’ve read there should only be two listed, namely:

‘Macintosh HD’ with it’s icon showing a small insert Finder icon (read only)
‘Macintosh HD - Data’ with it’s icon showing a small insert house icon (writable)

So clearly the 2nd ‘Macintosh HD’ and the ‘Macintosh HD - Data’ need to be merged into one called ‘Macintosh HD - Data’. How do I do this? I’m assuming once done I should then see only the one icon on my desktop named ‘Macintosh HD’ - correct?