> Any creation of affordable housing contributes to slowing down increasing prices.

As does creation of market rate housing[0], even in the short term.

[0]https://research.upjohn.org/up_policybriefs/13/

But it's obviously more effective to create more affordable housing.

> Many countries do this by putting legal limits against gentrification.

What does that even mean? I'm not aware of any country that restricts the change in the income mix of housing, or the renovation of dilapidated housing by new residents.

There are thousands of building regulations.

Here are few examples among some EU countries: setting a minimum density and number of floors in urban areas to prevent "mcmansions".

Mandated commercial areas (aka shops) on the ground floor on new buildings.

Requirements on walkability applied to new road design to prevent sprawls e.g. limit cul-de-sacs.

Minimum and maximum percentage of buildings for industrial / office / shop / domestic use.

Minimum and maximum apartment size.

Tons of limitations on renovation of historical buildings.

A lot of this stuff makes it very difficult to quickly transform an already urbanized area into a bunch of super-luxury villas or similar.

There you go, silent downvotes for providing information...