At half health, wither is supposed to dash and break 4×6×4 blocks at a time, and it works in 1.19. However, it breaks about 6×(80~100)×6 blocks from top to the bottom of the chunk in a flash. If this behavior is worked as intended, then wither in bedrock edition is tooooo difficult to kill in survival mode. I'll upload a video to demonstrate, and the full video with detailed information is here: https://www.bilibili.com/video/BV13V4y1b7ub