I contacted MS support for an issue regarding slow Power Query refresh. They requested to remote control my PC then, as a try to solve the issue, they reset Excel setting by deleting its Registry data.
The issue has not solved but I noticed later that I lost access to Power Pivot and it is not showing in COM add-ins list as well
I have tried Repair Microsoft 356 (Quick Repair and Online Repair) and it didn't resolve the issue.
Noting that Power Pivot add-in folder is exist in (C:\Program Files\Microsoft Office\root\Office16\ADDINS) as shown below
I have Microsoft 365 Family subscription version (Microsoft® Excel® for Microsoft 365 MSO (Version 2112 Build 16.0.14729.20254) 64-bit) on PC/Windows 10