After a deep search, testing systematically all options in my preferences related to network activity, I discovered that ESET Cyber Security (v8.X) is the cause of the problems.
Although every network filtering and firewall was disable, including real-time monitoring the VPN/Filter was causing the problems, to be more specific: ESET Network content filter.
After disabling this content filer and enabling it again, the IDE seems to startup.
This is not the first time that ESET causes troubles, I thought I knew them all by disabling them in the UI... but I just learned another option.
Apologies for raising this issue, and solving it at the same time.