Understand new icon in Android 11 call logs In the phone call log, what does the green network icon mean after I upgraded to Android 11?
Does that mean that the phone call went through the Wi-FI network instead of 4G/5G ?
Yes, this is voice calling over Wi-Fi but not related to Android 11.
I have a Pixel 4a, Android 11 with Wi-Fi calling enabled but do not see that symbol in call logs. I couldn't find any reference to it in the Android 11 changes.
Wi-Fi calling needs to enabled by a) carrier b) compatible devices. Both need to be compatible.  Probably your carrier, recently upgraded to this facility and hence you see this symbol. This symbol has been reported in call logs on certain devices four years ago on Galaxy S7 Edge. So, it looks to me like an OEM specific feature.
Related
What is this icon depicting a phone and Wi-Fi together?. You should see this or similar symbol when you are placing a call on Wi-Fi.