Some computer types double up the Fn key functions.
So for example, my F6 button with the Fn button will shut off my track pad. Without Fn, it’s just does what F6 is supposed to do.
With that in mind, there are computer makers out there, like DELL, that design computers for your Grandma. So instead of your Grandma hitting Fn and F6 to turn the track pad off. They make it the other way around. F6 will turn off track pad, and Fn F6 with do what F6 should do.
You can usually tell if you need the Fn key by looking at both the colour codings on the F keys and the colour of the Fn key. What ever action the colour matches, is what Fn key brings to the party.
I don’t think you’ll be able to change this, as in your situation, without the Fn key, your F keys might be hard coded.
Hope this helps.