I download Mullvad VPN but when it’s connected via anywhere but Australia i can’t even access lemmy via this account.
How are you acccessing the site? Is it via app or via web?
I can access https://aussie.zone/ via browser connected to most non-Aussie VPNs, but I will get a momentary "Checking to see if you are human". If you still can't access via that, it may be your browser/configuration.
In general, many web sites block VPNs. Eg with Reddit and other sites like youtube, it depends on a server by server basis if they are blocked. Eg, the Sydney ones rarely work, but some others in Australia do.