I am experiencing the same issue:
May I answer your questions, but please note that the error is generated by brave servers. No network issues, no DNS issues.
What are you looking for specifically, at the Brave.com website?
Anything under brave.com throws 503 with message " 503 ERROR The request could not be satisfied."
Subdomain community.brave.com seems to have no such problem.
What is your Computing Device Operating System version?
I can confirms it fails in MacOS, Android, Windows.
What is the Internet browser that you are using?
I can confirm fails with Brave, Chrome, and Opera.
Are you using a VPN?
Fails when not using VPN. The problem disappears when using VPN or Tor.
Looks like the problem arises for users of certain countries.