Disk utility stuck (MacOS Catalina)

Sorry, you are in deep trouble.

1] First lowest impact attempt:

hit [⌘]+[⌥]+[esc], select Disk Utility. then [Force Quit]

then shutdown the Mac.

2] If this 1st approach fail, then force a shutdown of the Mac with 5 seconds on the power button.

3] Boot in recovery mode: power on your Mac and immediately jump on [⌘]+[r].

4] Select "Disk Utility" from the macOS Utilities.

5] Select your core storage "Container disk3" and fire "First Aid" as you did previously, but now from a safer

environment. Plausible explanation: your "Container disk3" damages touched either system library used by Disk Utility

or Disk Utility itself or the OS itself.

Please report if this was of any use or if any problem appear.

If step 5] successful, then run "First Aid" on each contained disk: "Macintosh HD", "Macintosh HD - Data".

I hope you have some backups of your "Macintosh HD - Data".

From your negative return I conclude that even your recovery HD hidden volume is also damaged. But your problem is that

the partition exists.

To be honnest, this is rather bad news for your physical disk, I smell the smoke.

Just to know I am not just leading you to waste a full day for nuts,

how old is your internal disk? ( Don't be ashamed I am working with 10 years old Mac and disks :) ).

Then there exists 2 other ways to save your existing disk, if it's any worth for you.

If it was my disk, I would try it to know for sure if I am not trying to rescucitate a dead cow. There is nothing worse than

to work with a dead disk without knowing everything we do is corrupted and not recoverable.

1]. Use a full installer USB key. ( I recommend to always make and test one, because this is the fastest and safest recovery method ).

If you have another Mac able to run Catalina, you could be one. See here :

https://osxdaily.com/2020/07/14/how-make-bootable-macos-catalina-install-drive/

2]. Use the Internet recovery.

You will need a perfect Internet connection ( == not Wi-Fi and Wi-Fi off, i.e. Ethernet or Thunderbolt + Ethernet only ).

Next turn on your Mac and immediately jump on [⌘]+[⌥]+[r] .

Be patient, the nice planet will start to spin for ( from memory ) something around half an hour ( not sure, I usually

can't stay more than one minute in front of anything spinning to make me sleep ).

This recovery method from Apple servers will reinstall the original version which was the 1st factory installed.

1st thing to do: a full "First Aid" from "Disk Utility" ( 1. container, 2. Macintosh HD, 3. Macintosh HD - Data ).

Next reboot and hold your breath.