Realm world donwloads, but crashes in singleplayer

I can dowload latest realm backup to singleplayer, but the moment i try to play it in singleplayer, the world is blank, but no crash is reported. the world icon in singleplayer is greyed out too for all the realm world downloads. i wanted to add datapacks and reupload it to the realm, but cannot do so now.

The issue is the same in vanilla and modded minecraft.