macOS – Hard Drive Not Showing in Recovery Mode

macosrecovery

I was trying to go back to OS X El Capitan with Recovery Mode, but after agreeing to the T&C, it tells me to choose a HD where to install the update, but it doesn't show up. What can I do?
I'm currently running macOS 10.15.6 w/ my MacBook Pro (Retina, 13-inch, Early 2015)

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EDIT: This is what the disk utility GUI and what the diskutil list shows.
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Best Answer

'Going back' & 'update' are mutually exclusive terms.

You will need to re-format the drive to HFS+ first from Disk Utility. El Capitan cannot read or understand the APFS disk format that Catalina uses.

Your edit suggests you are still in Catalina & that your disk is currently APFS.
You will need to start from your external El Capitan boot medium [or from Internet Recovery] in order to be able to format your boot drive [you cannot format the drive you are booted from, for obvious reasons.]
Select the Physical disk in the left column [Apple SSD] & select Erase. Set to GUID/HFS Extended, Journalled.

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