I just built a new PC with a Ryzen 7700X, ProArt X670E, 32GB of DDR5-6000, and a RTX 3090, and I noticed that opening a second instance of an Office file can take up to 15 seconds. This wasn't an issue on my previous i7-9700K.
For example, I open an Excel sheet (it opens instantly), then I open another Excel sheet, the second one will take up to 15 seconds to open. But opening other file types like Word will be instantaneous.
It only seems to happen with Excel sheets, even very small ones with only one cell of calculations.
I have the latest version of Office 365 (v2209, Build 15629.20208) and all the latest motherboard and chipset drivers installed.