I hit the same issue recently and found a solution that works for me on macOS.
As you've already highlighted, this issue started with a Chrome update which is forcing SSL on localhost *.dev URLs.
To get around it you need to add the certificate to your keychain and override the trust setting:
- After creating the self-signed certificate through MAMP Pro, open a Finder window and navigate to the directory where you just created the certificate.
- Open Keychain Access. Unlock it for editing with your admin password if necessary.
- Click Certificates in the bottom left.
- Drag the .crt file from Finder into the Keychain Access window. You should now see the certificate appear here.
- Right-click the certificate (in Keychain Access) and select Get Info.
- Expand the Trust section.
- Next to Secure Sockets Layer (SSL) select Always Trust from the dropdown.
- Close the certificate info window. You'll be asked if you want to save the changes and authorise with admin password.
- Return to Chrome. Reload the page. Get back to work.