every solar attack froze the world and it makes the fight unenjoyable

“Ticking player”? Is that from a text log?

No, I mean the world stops for a moment every time the boss does that attack

...
wait what?
how do you know I have it? lol

Try removing radium.

Well, seems fixed, Is there a way to have Radium without this issues or should I remove the boss, because I don't have any problems with other mobs of the mod

Someone else reported this issue and told me radium was the cause.
Not sure yet, I have to do some research.

in its config you can possibly stop it from checking its mixing for example something like this mixin.ai.poi=false but thats not for mowzies

You can add mixin.entity.fast_retrieval=false to radium.properties in config folder to force Radium skip mixing in the entity fetch optimization as a workaround.