When I add a frame via “fx / Frames”, they are already very wide at the smallest width. Especially if, for example, I use the “White” frame to place just a thin line around the photo, this is already very wide with a value of “1”. Perhaps you could make the range adjustable in pixels (or better yet, as a percentage of the overall resolution of the image).
Feel free to vote for it if you like 
frame thickness beginning at 1 pixel, and color choice (any color) for frame would make this tool complete.
To make this tool complete it would be necessary to be able to change the thickness separately for each side, here
Ok, I see… DxO’s typical stubbornness in not really responding to customer requests… too bad 
One of the reasons why I only do DxO upgrades (if at all) on Black Friday or every two years (on Black Friday).
An other idea: add a thin frame of selectable colour when printing. This feature should be part of PhotoLab.