valet share, ngrok giving 404, CORS errors
I'm not 100% sure this is the answer to your issue; but this might be the solution:

Helge has written an article here about using ngrok with Craft CMS (which I'd recommend looking over if you haven't already). In particular, he mentions he has the following lines in his Craft config particularly for logging into the CP over ngrok:

// Logging in to the CP will fail unless you turn off CSRF protection.
'enableCsrfProtection' =&gt; false,


Try that config option and see if that fixes the issue for you...