My os is Windows 10.
I'm using ArcGIS pro 2.4 and I have purchased a personal use licence.
Since I registered by my Google account, I have to log in this way. Recently, when I have to use ArcGIS Pro on a new computer (my old computer works well), I found this issue.
c) I have cleared all cache and cookies on both devices. Same issue
d) I have uninstalled my Internet Explorer and set Chrome as the default browser.
This is one thing to explore - Bug: Unable to sign in to ArcGIS Online from ArcGIS Pro using Google credentials (esri.com)
Related - are you able to upgrade to the latest release of ArcGIS Pro 2.7? Many of these earlier 2.4 bugs have been fixed with later releases.