Saved files are not compatible between ZIsland UE4 and UE5 versions. If you want to play ZIsland v0.19 or higher or ZIsland Demo, please delete the "save folder" as previously commented
Viewing post in Z-Island UnrealEngine5 Demo comments
It's not, there 2 versions of ZIsland the UnrealEngine 4 version which is available here: https://gamingtalesstudio.itch.io/z-island
And an UnrealEngine 5 version (DEMO) which will contain more side quests content but less characters here: https://gamingtalesstudio.itch.io/z-island-demo =)