I have a Dell monitor which supports VGA - so I am using a VGA cable, VGA to HDMI adapter, and the USB-C Digital AV Multiport Adapter (Apple) to connect to my MacBook Air 2020 (running macOS Catalina Version 10.15.5).
However, the screen on my MacBook keeps flickering - in the Displays window (under System Preferences) I can see it detects the monitor and then loses connection very quickly.
I tried the same setup with an older MacBook Air 2015 (running macOS Catalina 10.15.4) - the only difference was that I did not need a USB-C Digital AV Multiport Adapter, instead I used a HDMI to Mini DP adapter. And it worked like a charm!
Is there any reason the newer MacBook Air would cause a problem?
P.S - to troubleshoot this better, I connected the MacBook Air 2020 with a monitor that supports HDMI with the Multiport Adapter and an HDMI cable - and it worked smoothly without any flickering.