What filler should I use for this mixed wall? (before tiling)

[Leaff]

I've removed all the old tiles because new mosaic is going up. You can see the result in the photo. My question is what type of filler should I use to make the wall smooth so I can put up the new mosaic. Even older tiles remain in one spot, in another the plaster has come off, and in some places the plaster and paint are stuck very firmly (without sounding hollow). It is a "dry" interior wall in a kitchen. No idea what type of plaster it is, but the house is over 100 years old, and the plaster is probably quite old as well.

 

[ToA]

I don't know if it's right but I would have put up gypsum boards instead of spending a lot of time plastering (I'm really bad at plastering) ;-)

 

[Leaff]

@ToA
It doesn't work as the wall protrudes too much, extends beyond the trim around the door, etc.

I bought Husfix today, a 10kg bag, and will plaster the wall tomorrow.