Screw broken off in the turbocharger

GAU: A screw has broken off in my turbocharger.

I'm currently cleaning the VTG because the distribution was clogged, and now...

How can I best get them out?

2. Who can supply this type of screw? M4 x 20 Torx 20 head (strength?)

This is a Garrett turbocharger with Variable Turbine Geometry (VTG) from a VW Lupo 3.0.

Weld the motherboard and then try to remove it.

I would heat the casing to 150-200 degrees and spray it with rust remover. First, secure the remaining bolt with locknuts, then try to loosen it. Welding is a second option, drilling is the third. Election.

...or pry it open with a screwdriver and manipulate it... it's best to heat it up beforehand.

Thank you for the tips!

The screw is now out.
I had something welded twice.
Every time, the screw breaks off.
I was already a bit grumpy.

A kind friend has now removed the stub and then smoothed out a slight indentation.
Then, I drilled out the screw using a 2mm drill bit.
fumbled around, broke off a tap.
but then, eventually, they succeeded.

Great! Saved 450 euros!