Don't think I have ever seen haloing that bad on a GBA screen before, much less a 101. Usual causes here are a backlight decides to lose the plot (though that is usually dim spots rather than blown out) or the screen layers are delaminating somehow and the layers that diffuse the light around no longer do.
For the latter then does pressing reasonably firmly on the screen make a difference?
If it is not a device with a bonded touchscreen then there is limited stuff a normal person might be able to do here*, unless it is a simple mechanical wrap at the edge that is coming loose (don't know what goes here). There appear to be a few dead pixels on the sides as well, which could be related or could just be a sign of a bad screen -- at first I thought it might have been a stripe of halo rather than a gradual thing which would be different to what I normally see, but still reasonable. To that end replacement screen time. 101 screens can be found -- many like to upgrade their older SP with one or stick one into an original GBA, or if you can find a 101 with a bad shell or bad motherboard you could do a shell swap/non screen gut swap as appropriate.
*for other devices then some have tried injecting resins into the gaps and it has yielded some improvement, or at least slowed decay, but as far as getting even a 90% screen again you would be lucky. Breaking a screen down into layers and then rebonding everything in some ways is easier, but you will start needing to have dust free environments for that one and cost wise you are not going to beat a replacement screen, or indeed a whole brand new 101.