I have same problem but It’s not saying nginx. It’s just blank window popup then disappear.
I don’t want to wait a fix, I just disable connectivity check until there is a fix.
sudo tee /etc/NetworkManager/conf.d/20-connectivity-fedora.conf <<EOF
[connectivity]
enabled=false
EOF
Sure, but until we can figure out whats going on, it’s unclear what the
fix will be. 
The’s likely more than one possible cause for this issue.
In other words, it could be a different issue for each person/network.
I haven’t seen this happen for a while now, either with just Ethernet, just Wi-Fi, or both. I couldn’t say which update to which package fixed the issue, but it does seem to be fixed now either way, at least for me.
I’m experiencing this as well under fedora 39 with gnome. I’d say the check would make sense if it was headless. Having a popup flash on the screen each time internet connectivity is checked is a tad annoying tbh.