from private message I bring into public domain, no where did I say disable it, there should be an upgrade available (also see if upgrade notice in module manager).
I see several issues, 1) add to cart can fail, I had same issue with 9.0.0 and jumped to 9.0.1, this for client upgrade 2) prestashop checkout has always been an issue, there is update to this make sure you have it
https://addons.prestashop.com/en/payment-card-wallet/46347-prestashop-checkout-built-with-paypal-.htm
alternative, based on your payment options (what are they?), is to uninstall prestashop checkout, use native ps checkout and install payment modules, for example paypal and stripe. to be honest over the years I've invoiced thousands of dollars to new client intake with checkout issues, removing ph checkout or other 3rd party checkout always solved.
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what I did not say in private but probably up above, there are major issues fixed in 9.0.1...I suspect there will be another release 'very' soon to solve some other major issues.
1) create a subdomain and create a staging copy of your current shop 2) back staging copy up 3) try to upgrade to 9.0.1 using prestashop upgrade module.
this is your best option...tip: also when you search for issue you are having frame it 'prestashop github (describe your issue), you will not be first person to have it and mosT often you will find issue already reported in github. The forum is good place to have someone hold your hand but ps devs do not monitor or participate here.