In case is useful for anyone: I've finally fixed my Kobo Aura HD, it turned out it was a broken screen. I just ordered a replacement from AliExpress. The specific model is this and it worked like a charm!
https://es.aliexpress.com/item/32493...26d463c055EDkw
Be warned that opening the kobo it's kind of hard at first because it's glued inside (horrible desing to avoid repairments)!!