Weird situation I have seen others complain about online – their WordPress Woocommerce product pages having the PayPal button greyed out.
Not on all products – but only products with variations.
Here is the solution – set a default variation to show customers.

On your product page go to:
Product Data | Variations | Default Form Values
Set a default variation and, at least from my experience, that will make the PayPal button appear again – usable and in full color.
PayPal Button Greyed Out on Woocommerce Variable Product
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