Can't say without seeing the results, as to the cause of the flicker. The AI denoisers are more prone to give different results frame to frame than the Corona High Quality, so the High Quality is recommended. If using a Cache, try using the other one (if using UHD try 4K, if using 4K try using UHD). Be sure to have Flicker Free set. It is not impossible that the cache will flicker even then, in which case you can swap to Path Tracing. But there could be other things going on, depends on the type of flicker (Cache flickers tend to be shadows that are darker or lighter in different frames - there can be "flicker" from reflections too if something has high glossiness and is reflecting some sharp point of light, and so on)