Thrust won't be an issue if push comes to shove China can import NK32 or NK25 as interim solution even J20 used Russian engine at first more over the aircraft is expected to enter service in 2025 that's a lot of time look at where China's engine industry 5 years ago and the progress made until now critical techs have already been learned, it's quite doableThe B21 uses a F135 derived engine. You can't compare that with the engines China has available right now.
The F135 has 128 kN dry thrust. Compare that with the numbers we have been discussing above like 77 kN.
That is why the H-20 should have four engines.