How do I delete just my Gmail without losing my whole Google account (Drive, Photos, YouTube)?

Yes, you can remove just the Gmail service and keep the Google account (Drive, Photos, YouTube) alive, they're separate. Go to myaccount.google.com > Data & privacy > scroll to 'Delete a Google service' (NOT 'Delete your account') > re-enter your password if asked > find Gmail and hit the trash icon. Google then asks for a new non-Gmail email to sign in with going forward, since your login was the Gmail address. After deletion: emails sent to the old address bounce, and it's gone for good, nobody can reuse it. Download anything you want first with Google Takeout. Delete the WHOLE account instead and you lose Drive, Photos and YouTube too, so pick 'Delete a service'.

The critical distinction: 'Delete a Google service' removes only Gmail; 'Delete your Google account' nukes everything. Pick the first or you'll lose Drive, Photos and YouTube with it.

Export first with Google Takeout, once Gmail's deleted the emails are unrecoverable and anything sent to that address bounces. And you'll need a non-Gmail address to log in afterward, so set that up before you start.