Hi, @Ola_Sjostrand.
Unfortunately, there really is no way to get the Linn remote to support transport controls when using Roon as a source. Many Roon users use other strategies that do allow for, at minimum, play and pause controls.
I personally use rooDial, which you can read about here: rooDial a Wireless Volume Knob for Roon with Microsoft Surface Dial
rooNuimo is a similar option, though the hardware is more difficult to acquire. Deep Harmony is another option - it enables use of a Logitech Harmony controller. These options all require a bit of tinkering but are very manageable if you’re interested.