The disappearance of your custom themes in Theme Park after a major One UI upgrade is a known issue, often caused by compatibility changes between software versions.
Here are the steps you can take to try and recover your themes and icons:
1. Reinstall Theme Park
Sometimes, simply reinstalling the Theme Park module after a major OS update can resolve glitches and force it to re-read its data.
Uninstall Theme Park from your device.
Reboot your phone.
Reinstall Theme Park from the Galaxy Store.
2. Check "My stuff" in the main Themes menu
While Theme Park creates the themes, they are generally stored within the main Samsung Themes application's database.
Open the Settings app.
Navigate to Themes (or press and hold on an empty spot on your Home screen and select Themes).
Tap the Menu icon (usually three horizontal lines or dots) in the bottom corner.
Select My stuff.
Check the Themes and Icons tabs for your previously created elements. They may be listed there, even if they aren't showing in the Theme Park app itself. You can try reapplying them from here.
3. Re-import or reinstall the saved APK files
You mentioned saving some icon themes as APK files. Since One UI 6.0/7.0, Samsung has made changes that affect how themes and icon packs from external sources (including self-made APKs) are handled, sometimes limiting their full functionality or requiring specific workarounds.
Try to install the APKs again: Locate the APK files on your phone's file storage and attempt to install them. Ensure you have allowed installation from "unknown sources" for your file manager or browser.
Check compatibility: Be aware that older APK themes might not be fully compatible with the new One UI 8.0 framework and may not apply correctly to all system elements.
Use a third-party tool (Advanced option): Some users in community forums have reported using tools like "Canta + Shizuku" to restore deleted theme data, but this is an advanced method and may require some technical know-how.
4. Wait for a Theme Park update
Major One UI updates often break aspects of Good Lock modules like Theme Park until the developers release a compatible update. Samsung is likely aware of any widespread issues and an update should be available soon if not already. Check the Galaxy Store frequently for updates to the Theme Park app.
If all else fails, and the data is still not visible, you may need to recreate the themes using the updated Theme Park app, as the underlying structure for themes might have changed in One UI 8.0.
Online search brought this up, hope you find something useful that will help.
