I don’t use decluttering card anymore as I have shifted towards lovelace_gen. The same goes for markdown cards. I only use markdown cards without styles as they otherwise take way too long to load. I can only suggest removing border radius and box shadow if you want better performance. Or alternatively use a button card to mimic the markdown card. This should be relatively easy.
In my personal setup all notifications are done with button card now.
And I use markdown merely for instructions