Derived compare-at prices are now hidden in Europe for compliance with the European Price Indication Directive
To protect merchants from unknowingly violating the EU Price Indication Directive, compare-at prices set for a country outside of the European Economic Area (EEA) are no longer shown to EEA markets. This is only available if you are using Shopify Markets to adapt your store, but works whether or not you are using Shopify Payments to sell in Euros.
This only affects all merchants whose primary market is outside of the EEA. If your primary market is in the EEA, compare-at prices are always shown. You should take care to set them in compliance with the directive.
Merchants with a non-EEA primary market who wish to show compare-at prices to EEA customers can do so by explicitly defining values for those markets via the product CSV import function. Alternatively, you can opt out of this functionality entirely by going to Settings > Markets > Preferences and unchecking the checkbox for "Hide compare-at prices for European Economic Area (EEA) customers".
This content doesn't contain, and isn't meant to provide, legal advice. You should consult your own legal counsel to determine how the laws in your region and the regions in which you sell might affect your business.