The toilet was running from the first day, at first I tried to see if it was a bad installation, but nothing. Then I called Ideal Standard, where the technician came within 2 days, changed the bottom rubber from the mechanism which had a flaw (material defect) and with certainty that this would solve the problem, he left.

Of course, it didn't solve it! Sometimes it runs - sometimes it doesn't, sometimes the float gets stuck... The leak is due to the Rimless feature and because the toilet has a slight inclination depending on the tiles.

The problem was solved by purchasing and installing a NEW mechanism, definitely NOT Ideal Standard. I bought one from the company Nicoll + the mechanism:
WATER SAVING ADJUSTABLE HEIGHT MECHANISM Universal 3V10S
FLOAT FOR TOILETS SIL30 or SIL50 depending on the inches of the supply (https://www.skroutz.gr/s/26253545/Φλοτέρ-Χαμηλής-Πίεσης-Ορειχάλκινο-3-8-Κάθετο-SIL30.html)

Quiet, start-stop with multiple settings. Simply a perfect mechanism. I am not advertising for this particular company, I was just looking for a quiet mechanism, half - full flush and start-stop for even less water and I came across it.

It seems that the Float and the mechanism from Ideal Standard didn't work... It failed!! So if you buy this beautiful, in my opinion, toilet, keep in mind to also buy another mechanism.