Can't add Google account to secure folder

[gsxdsm]

Can't add a Google account that is already on the device to a secure folder. Can't access Play or installed apps licenses. 

[carlosbxx]

I use my own domain so I couldn't use just the username without using the @Gmail.com. IInstead I chose the option saying I didn't know my account and used phone number and name/surnames to log in which added the account and it's all good now.

None of the other options worked. 

[Anonysillymouse]

I can add Gmail, Yahoo Mail and Files Apps  in my secure folder,  but I can open them as always from my Apps menu.

I wanted to add an extra layer of security on these 3 apps. However it's pointless having them in Secure Folder if you can open them otherwise from All Apps. 

How does one resolve this ?