What kind of landing gear does the Y-20 use ? Because both the ARJ-21 and the C-919 uses foreign made landing gears. And those are both lighter planes than the Y-20.
"What kind" as in whether they're produced in China or not?
Keep in mind that ARJ-21 and C919 both have many foreign components, because they're commercial products meant for commercial buyers.
The likelihood of anyone outside being willing to sell China landing gear for Y-20 is very small indeed. And given the industry's previous experience in making landing gear for larger legacy aircraft such as Y-8/9 and H-6, developing brand new landing gear for a 220+ ton MTOW aircraft is well within the bounds of capability, especially if Antonov assistance was there.
The fact that they are using foreign made landing gear for C919 may not be related to whether China can produce good landing gear for C919, but more to do with having a more reliable supply chain, or having more foreign made subsystems to build a greater sense of "reliability" in the aircraft for commercial sales... small differences in reliability, cost, as well as perception are all very important for commercial airliners. I think that is why C919 features so many foreign subsystems from glass cockpit to landing gear, even though the indigenous industry can likely develop similar products as well.
In other words: military and civil/commercial projects differ in their requirements many of which are not inherently based around "capability", and if a country or an industry can produce one subsystem or one type of subsystem for a military project it does not mean it will necessarily be suitable for a civil/commercial project... and vice versa.
Another caveat: just because one nation is using another nation's subsystem in lieu of their own for a specific project, it does not mean that they do not have a competitive product or the ability to produce a competitive product... it just means that for that specific project, the other nation's subsystem is considered a better fit. for instance, the USN is intending to fit the European CAPTAS sonar aboard their LCS as part of the ASW module -- that doesn't mean the US industry is unable to develop competitive variable depth sonars or that the lack the capability to, it just means that for the LCS project specifically, the European sonar is considered the best fit to the project requirements.