I just formatted my macOS big to install Catalina. At the point of APFS format, I don’t know which one to chose
How to boot my MacBook Pro from usb flash to install Catalina
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Personally I would click on "View" within Disk Utility and select "Show All Devices" so that the physical drive appears on the left pane of Disk Utility. Then erase the physical drive as GUID partition and APFS (top option), then quit Disk Utility and select "Install macOS". Here is an Apple article showing how to reveal the physical drive and erase it:
https://support.apple.com/guide/disk-utility/erase-and-reformat-a-storage-device-dskutl14079/mac
This assumes that your Mac is capable of running Catalina and did not ship from the factory with Big Sur.