I was playing MC Java (22w44a), and I used a command, and the wither was invisible. The WitherInvisibleWither.jpepart is the wither, and the WitherInvisibleCommand.jxris the command. If the image doesn't load, (for whatever reason,) this the command: /summon minecraft:wither  ~ ~ ~ {Invul:25000,CustomName:Grumm}

I found this on Bing.

But, if you want to see the video, you can find it on YouTube.

Actually, it just took a loong time. But I guess that's a different bug. (Or my PC is broken.)