On IMAC M4 (Sequoia 15.3) cannot access my subscriptions

Please explain what you mean by “cannot access my subscriptions”. Are you having problems launching an app you subscribe to? Are you trying to manage your subscriptions (make payment or cancel). What are you doing to access your subscriptions? Do you get an error message or warning? Please be specific.

To manage your subscriptions

System Settings->Apple Account (your name)->Media and Purchases->Subscriptions->Manage

From there you can renew, cancel your subscriptions.

So why did you not make that clear In your original post? We cannot be “helpful" if we don’t know what’s going on. Some basic information needed.

1. Is your iMac connected to the internet? Can you navigate the web, receive email, etc.?
2. Are you logged into the same Apple Account that the subscriptions were started with?
3. Are you running any kind of VPN or Anti-virus software, often the cause of “can’t connect” problems?
4. Have you tried restarting your iMac in Safe Mode. Safe mode performs certain maintenance functions like emptying caches, etc. When in Safe Mode try accessing your subscriptions. If all is okay restart in normal mode and test again. If still not able to access then something may be wrong in your iMac account.

Start up your Mac in safe mode - Apple Support

So tell us whether you are running anti-virus software or a VPN, both of which would be disabled in Safe Mode. If the answer is no then try logging out of your Apple Account and then log back in. Test