Can a Mac OS Extended formatted SSD drive be opened in later macOS versions?

werdup wrote:

In order to update the formatting to (APFS) I assume the drive would be wiped clean. Correct?

You can convert an HFS+ volume to APFS. Within Disk Utility on one of the menus there is a "Convert to APFS" option when you have an HFS+ volume selected.

Before you attempt the conversion, make sure you have a good backup of the data on that drive just in case something goes wrong.

FYI, if the external drive is a Hard Drive, then it may be best to leave it with HFS+ since APFS tends to cause extra wear on a Hard Drive. If the drive is an SSD, then APFS is fine since APFS is optimized for an SSD.

Yes.

Recent versions of macOS want the startup drive to be formatted using APFS, but have no problem reading from or writing to HFS+ volumes.

macOS Extended Journaled was the required format for Mac boot drives up to 10.12. It was also the default format for boot drives in 10.13 & 10.14 if the drive was a traditional HDD.

Apple File System (APFS): The required format for Mac boot drives in macOS 10.15 and later. In macOS 10.13 & 10.14 it was applied by default if the boot drive was an SSD.

All Macs since the advent of OS X can read & write macOS Extended format drives.

Reformatting will wipe the drive.