There are several ways of booting Linux in a system where you’ve installed OpenCore Legacy Patcher.

The one that best suited my needs was this one, and allowed me to end up with the following boot menu:

OCLP boot menu

Please be aware that you must provide the file ext4_x64.efi that is mentioned there, and put it inside folder /EFI/OC/Drivers .

That driver can be found on any distribution of rEFInd.

At the same time, you must modify the file EFI/OC/config.plist and add the two following driver sections:

            <dict>
                <key>Arguments</key>
                <string></string>
                <key>Comment</key>
                <string></string>
                <key>Enabled</key>
                <true/>
                <key>Path</key>
                <string>OpenLinuxBoot.efi</string>
            </dict>
            <dict>
                <key>Arguments</key>
                <string></string>
                <key>Comment</key>
                <string></string>
                <key>Enabled</key>
                <true/>
                <key>Path</key>
                <string>ext4_x64.efi</string>
            </dict>

Be aware, as well, that if you reinstall OpenCore Legacy Patcher (because you wanted to update its version or other reasons), you must repeat the process.