At the moment, Microsoft has a list of ten issues that it's investigating. Nine of these known issues result in a "compatibility hold", which means Windows 10 May 2020 Update will not be installed via Windows Update until Microsoft resolves the outstanding issues. Of course, users can still force the update, but this is not recommended.
The Verge checked compatibility on several devices and concludes that Windows 10 May 2020 Update is not compatible yet even with some of the company's own hardware:
We’ve tried to check for the update on a variety of devices at The Verge, including Microsoft’s Surface Book 3, Surface Laptop 3, Surface Pro X, a gaming laptop, and two custom-built gaming PCs. We’ve only been able to successfully install it from Windows Update on a Surface Pro 6.Presumably, the issues will be resolved over the coming weeks and months.