will be quite time consuming if you have to do that for every single theme. I have similar problems with every single theme on poco f3 since the last two xiaomi.eu updates but staff member Igor says that it is just my own problem then...Fix Themes
1.- Extract the theme you lost compatibility, you can use MIUI theme editor to extract.
2.- Open mtz generated (prefer with pc)
3.- Open description.xml
4.- Change Value of uiVersion to 12
5.- Replace <version> line to <miuiAdapterVersion><![CDATA[2.0]]></miuiAdapterVersion> (This help to compatibility warning message when you apply a theme)
6.- Save or update with mtz file with the new description.xml file
7.- Delete old theme, and import new theme.
8.- Apply