Anyone have the experience from converting the condo 5m² yard to another toilet with WC, shower

how do you connect the poo pipe?
you will likely need to get your lower floor neighbour approval becaues you will be drilling and piping at their ceiling

Shower with a wash basin possible. Do water proofing to avoid water leaking to lower unit.

That why, was looking to see anyone had experience with this.

It is still possible to do.
You will need to raise the whole yard floor to accommodate the poo pipe.
And it has to flow to the nearest existing toilet.

When you raise the wc floor, you will either need to put a tall barrier or raise the floor of the entire unit. If new unit still possible. If already staying will be nightmare.

Shower is easy. Just get those ready made ones from homepro.

Unless no intention to sell off forever.