There's a discrepancy between the docs and the hints in Advanced settings.
The public docs suggest that the US region uses these ranges:
3.77.79.248/30
35.90.103.132/30
44.208.168.68/30
And then 3.77.79.248/30 is listed again in the doc for EU.
When looking at the Default Retool outbound region for queries in the Advanced Settings menu, the hints specify that 3.77.79.248/30 is indeed for EU, and the other 2 are for US.