Another way to open Windows 10 startup folder is to use the Run dialogue:

Press Win+R
Type

shell:startup

Click OK or press Enter:

If you wish to set a program to run on startup for all users accounts, create its shortcut in common startup folder. In Windows 10 its default location is:

C:\ProgramData\Microsoft\Windows\Start Menu\Programs\StartUp

You can open it by the path: %ProgramData%\Microsoft\Windows\Start Menu\Programs\StartUp or using the Run dialogue as we explain below.

Press Win+R.
Type

shell:Common Startup

Press Enter:

You can also add Modern apps from Microsoft Store to startup folder. Follow the steps:

    Open the startup folder: press Win+R, type shell:startup, hit Enter.
    Open the Modern apps folder: press Win+R, type shell:appsfolder, press Enter.
    Drag the apps you need to launch on startup from the first to the second folder and select Create shortcut:  ///

If error message "cannot create shortcut here, create on desktop instead?"
then

Create shortcut on desktop, copy to all users startup folder [shell:common startup] and accept UAC prompt. Can be edited later, just accept UAC prompt.