FYI, with some part replacements on a 2018+ Mac it is sometimes necessary to reprogram the T2 security chip/MLB to work with the replacement part. While the part may sometimes function at a basic level, there may be some side effects of not having it reprogrammed. Some Apple laptops require the reprogramming when replacing the Display Assembly while others do not. I believe your MBAir is supposed to have the T2 chip reprogrammed. Each part on these newer laptops have a part serial number which Apple programs for the T2 security chip. Apple claims this is about updating the HDR information and possibly other component specific information of the part, but I think it is all about making tracking the parts and being able to claim a secure path for third parties such as media services that want to be able to only provide HD content to devices with a secure path (it is not about user security, but about third party companies' fears of people misappropriating the content & services) since it should certainly be able to gather the part details such as HDR through other more normal means.
Unfortuntely it is impossible to reprogram the T2 chip/MLB even for Apple or an AASP unless the they actually performed the repair themselves since their service portal needs to associate the new part serial number with the laptop for their online service calibration tools to work. They could not help you at this point even if they wanted to help unless they ordered the replacement part through the Apple service portal themselves.
Or it may be that the replacement part you installed is bad, or there may be some other issue such as bad video cable, or bad Logic Board. It is really hard to say.
