Pretty sure there is no way through the login without accepting… however I’m not a tech guy.
Is time on your side?
If it is you could write to whoever administers mygov and let them know you need access but don’t accept t&cs. Ask them how to proceed. Ask if you can be forced to accept t&cs or if informed consent in needed.
If this is something you are being ‘compelled’ to do against your wishes and are being told there is no other way then it is clear you are being coerced into agreeing. You could choose to hold your ground and not proceed if forced to accept, however that may have other implications for you.
You could contact their tech support and notice them of a problem. Something like: “My login isn’t working”. “Everytime I try and login it doesn’t let me through. It asks ‘do you accept…’ and when I say no everything stops working.” It would be interesting to see their response to this. “But you ‘have’ to accept.”
You could also proceed to accept under coercion then write a letter noticing the authority that you proceeded under coercion. They won’t care however you will at least have a record of it.
Don’t know if any of that helps.