Access denied to irs.gov trying to check where's my refund

I have been getting this error after I try to check my refund status on irs.gov from my iMac using Chrome or Safari:

Access Denied

You don't have permission to access "http://sa.www4.irs.gov/irfof/IRServlet?" on this server.

Reference #18.b57a4217.1653852902.4c35d8c3

I've tried without VPN, with VPN, using Chrome or Safari, and still no way to get through. I can get to this site from another my mac laptop on the same Wi-Fi network but not from the iMac.

I was able to access this same irs.gov page from this same iMac a few months ago but at some point, it stopped working. Any help you can provide would be much appreciated.