Welcome to MFK.
Nice looking flowerhorn you got there.
I wouldn’t add severum in with a flowerhorn.
Severum are not nearly boisterous enough to handle even a mildly aggressive flowerhorn.
My advice would be to keep it alone or add some tough fast swimming dithers.
Giant danios or maybe Tiger barbs could possibly work.
I think adding another cichlid would eventually end in either the flowerhorn or the new cichlid being damaged or killed.