Unluckily not just venting. But so "pissed off" yesterday that indeed I did not provide enough info. Sorry.
To test, I use the sketch from the Blynk example: "Seed Ethernet V2.0". So this should not be a problem related to my project.
I tried with the 3 Blynk.begin() possibilities of this example:
(auth is correct)
Blynk.begin(auth, "blynk-cloud.com", 8442);
Blynk.begin(auth, IPAddress(192,168,1,100), 8888);
Connecting to Blynk server (no local server).
Tested on 2 different Arduino Mega and 1 Uno with 2 different Ethernet cards and 2 internet cables to exclude hardware issues.
I tried with a connection to my office router: TP-Link (TL-WR1043ND) or directly to the main connection from the internet provider "box"
(All firewalls off)