I neither use Logic Pro 10.6.3 nor Catalina 10.15.7. But it should be quite similar.
I would start with No. 3. If there is no IAC Bus available for you, start from 1 to 3.
1. Open Applications > Utilities > Audio Midi Setup.
• In Audio Midi Setup: Windows > Midi Studio.
• Double click IAC-Driver Object
• enable Device is online
2. Boot Logic.
• Go to Windows > Open Midi Environment
• Choose Layer > Midi Instruments (Top left)
• If empty, New > Multi Instrument
• Select the new created Multi Instrument object.
• Choose Port > IAC Driver (left)
• activate the channels 1-16 one-by-one by clicking on the crossed-out numbers on the created Multi Instrument
• rubberband-select the whole Multi Instrument and rename it to e.g. IAC Bus 1
3. In Logic's Main Window Create New External Midi Track
• Choose your IAC Bus 1, you can select different midi channels.