To be honest. I've not managed to understand which updates can and cannot be uninstalled. I just uninstall the most recent update and try to run FSX. If FSX works then great, if FSX does not work then I uninstall the next update and continue.
It seems random to me. However, with all the testing I have done, the API.dll error is almost definitely caused by Windows 10 22H2 updates.
It would be great if Microsoft could release a fix so that FSX worked correct as it did on pre-April 2023 versions of Windows 10 22H2.
If you are also struggling with the API.dll error on post-April 2023 versions on Windows 10 22H2, then please submit a support ticket to Microsoft here: https://support.microsoft.com/en-us/home/contact?SourceApp=smc2&ContactUsExperienceEntryPointAssetId=S.HP.SMC-HOME