Startup Folders

It is possible to use another folder as a startup directory.
You can check the exact location of these folders from (File > Options > Trust Center)
Select Trust Center Settings and display the Trusted Locations tab.

xlStart - Personal folders

Excel 365 - C:\Users\"user name"\AppData\Roaming\Microsoft\Excel\XLStart\   
Excel 2021 - C:\Users\"user name"\App Data\Roaming\Microsoft\Excel\XLStart\   
Excel 2019 - C:\Users\"user name"\App Data\Roaming\Microsoft\Excel\XLStart\   
Excel 2016 - C:\Users\"user name"\App Data\Roaming\Microsoft\Excel\XLStart\   

xlStart - Machine Folders

The exact locations of the xlstart folders will depend on which version of Excel you are using.

Excel 365 - C:\Program Files\Microsoft Office\root\Office16\XLStart\ 
Excel 2021 - C:\Program Files (x86)\Microsoft Office\Office16\XLStart\   
Excel 2019 - C:\Program Files (x86)\Microsoft Office\Office15\XLStart\   
Excel 2016 - C:\Program Files (x86)\Microsoft Office\Office15\XLStart\