I held off on upgrading Magento to 2.4 for several years, and now I have to do it because of changes to the UPS API; one module we have, uGiftCert, cannot be purchased or updated anymore, and I am a couple of versions behind the first one that supported Magento 2.4; since upgrading, I noticed that we cannot view orders in the admin area, and the culprit seems to be this module.
I would like to continue using it, but I don’t know what sort of things to look for to make this module compatible with Magento 2.4; I’m currently planning to write my own module that depends on Unirgy_Giftcert and uses preferences to replace the problematic PHP files with ones that work with Magento 2.4.
As a crude workaround, we could just find a new gift-certificate module and somehow migrate the existing certificates to the way the new module does things.