Magento is known for its frequent updates and changes, which can sometimes cause compatibility issues with custom integrations such as payment gateways. However, with each new version of Magento, the platform strives to maintain backwards compatibility and minimize the impact on custom integrations.
That being said, it is always recommended to thoroughly test any custom integrations after upgrading to a new version of Magento to ensure compatibility. It is also important to keep in mind that Magento is a complex platform with many moving parts, so even small changes can have unintended consequences.
In general, it is best practice to work closely with a Magento development team that has experience with custom integrations to ensure a smooth and successful upgrade process. By following best practices and keeping up with the latest updates and patches, it is possible to maintain a stable and reliable checkout/payment system on Magento.