No Byzantine Civil War of 1341 would be a big help. Keeping the Byzantine Army strong and the navy powerful would be huge as if the Ottomans cannot get into Europe, they will be destroyed in the Turkic Wars related to the Timurids and eventually internal strife. If the Byzantines keep Greece, and keep the Balkans relatively friendly while slowly building back up to the Danube, I can see them surviving for quite some time and maybe even reaching nation state levels of stability. Civil Wars have to stop, which they could as long as the Emperor recentralizes everything (doable if you have a strong army and supportive church) and curbs the nobles power.
Ultimately this comes down to the fact that the Ottomans were an unspectacular Turkic Tribe until the crossed into Europe and gained resources set them apart. If they are stuck in a disunited Anatolia, they would not survive the trauma of the Timurids attacking.