The more important question is the timeline of the thing. If the first flight took place last year, the MiG-29 project implies it'll take 5 years for this to be introduced and enter the hands of export partners, or 2025, or possibly 2023 if the Indians get LRIP.
We still have a number of questions about this aircraft. It seems to be running Izdeliye 30 based off the nozzle measurement and geometry, but we need to have an idea of how good the stealth coating, the sensors, and the radar is. But let's say it's the real deal, an aircraft with stealth in the same range as the F-35, or quite likely, better.
In that regard, China has a few options available, sorted in implementation time:
1: Build HF counterstealth arrays in Tibet and Pakistan. HF is still the gold standard and at very low frequencies, is likely to detect B-21s or even B-2s. This is expensive, but doable with existing technology. (2021,2022, now)
2: Fast track the FC-31. While the airframe is underengined and is suffering from either range or payload problems, it's the closest China has for a 'pure stealth' fighter. It won't fully counter checkmate or the F-35, due to its twin-engined design, but it's a good stopgap.(2023,2024,2025)
3: With the J-20 having WS-15 come ready, fast track the J-20's strike versions. This will likely be tailless, relying on TVC for high AoA and yaw, representing an upgrade in stealth which will likely be better than that of the FC-31, except that the J-20 is a larger platform and thus intrinsically less stealthy. (2023,2024,2025)
4: Accelerate the development of Chinese laser weapons. Mature laser paradigms in aerial warfare can potentially defeat the stealth paradigm. (2025,2026,2027)
5: Work on China's own F-35 killer. A JF-17-sized platform can potentially be upgraded to 6th gen or near 6th gen levels of stealth. A sixth generation JF-17 can potentially present a counter as well to NGAD, pending laser maturity and the end of stealth as an emphasis. (2027,2028,2029)