hmm... that's kind of an interesting use case, generally we cannot force Paypal to take a CC or not since we are using Paypal Express (at this stage) and we were counting on the CC gateway to handle CCs since checking out through Paypal using a CC only adds extra fees for both sides.
What I believe is happening is that Paypal gives you the option to login, when they see that the device has some cookies or IP indicating it has been used to access your Paypal account, thus they are trying to optimize the experience for you, if you try to checkout on an incognito device or Edge or a different browser mostly Paypal will give you the option to checkout without login in or creating an account.
I personally haven't had the chance to miss with those settings, but try looking on your business setup on Paypal and see if anything helpful in there
I'm open to suggestions and feedback for best ways to capitalize on the case above
Hope that helps!