I have some questions regarding the Ford Focus ST(2019 2.3 ecoboost).
Correct me if i am wrong but the RS with the same engine had some issues(blown head gasket and more).
My question is, did they fix that issue on this engine(since what i know is that this ST has the same engine) with the head gasket or those known issues or they still continue to suffer from those.

The headgasket thing was fixed a few years ago. I believe the affected models were recalled.

They're not the exact same engine though.

The issue with the RS was that some models had the incorrect head gasket fitted. The RS is supposed to have an uprated gasket to cope with the higher power output, but the standard gasket was mistakenly fitted to some cars. 
 

In the ST the engine uses the standard gasket as it’s running in a lower state of tune. So there are no worries of the same issue. 

I read a piece on this a couple of years back (as usual, can't remember where or find it now!😀).

Anyway, according to that article, certainly a head gasket issue, but apparently 2.3 Mustang head gaskets were incorrectly used in the failed engines. Although outwardly similar, there are differences in the coolant passages between Mustang/RS engines and using the Mustang gasket in the RS blocks some of them.

 

The engine in the mk4 ST is the Mustang variant not the RS variant.

I've never heard of the Mustang variant having any failures.