Hello @claireifilip,
Thanks for reaching out to the Roku community!
Based on the image you submitted, it appears to be a hardware issue, and we recommend contacting the manufacturer of your Roku TV for more assistance. Each Roku TV manufacturer provides direct support and warranty services for their products running the Roku OS. Since your affected device is an Onn Roku TV, we suggest reaching out to Onn support to report the issue and for further help.
You can contact them here: onntvsupport
Regards,
Karla