If i keep my liner bare and flat, and put the yellow irises in pots is there still a potential that their tubers and roots will damage my liner and how exactly does this work that they damage the liner?


How about catails?

If you check the pots at least twice a year, there shouldn't be a problem. My iris usually burst the pot from the sides. If they burst down or grow down, the pressure over time may compromise the liner. I worry about that but it still hasn't happened. Regular cattails really grow fast and burst pots.

if they burst the pots: how do the roots harm the bare liner having no gravel

They wouldn't normally but over time, the smaller filaments of the roots may penetrate the rubber as well as the larger roots simply pushing on it, creating strain on the liner. If it gets too thin, it will get a hole or split in it.