There are long old discussions about this. Watch for install options during install but remember that some apps like Office still place files on the C drive. And all apps drop registry entries on C so no one installs entirely on the externals.
Again, watch for the drive option when installing and change it when you can.
I used to store all my programs in my internal SSD Drive. I have purchased a Samsung portable external SSD drive which plugs into a USB 3.0 port. Can I install programs on this drive also?

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