In Chinese forum has some posts about this issue, it's about the version of themes app. Current version of themes in MIUI 12.5.6 stable is 1.9.3.1 (device: Poco F3), this problem can be easily solved by updating the themes app to version 1.9.9.1 in Chinese MIUI, but in xiaomi.eu updating a system software by using a apk is not possible. Hope developers can solve this problem in future update.