I have my own fabric server and installed this mod there to get rid of such cases (screenshot) or from endermen in the nether with blocks in their hands, but this mod did not help at all, these mobs stood with objects and still stand

I would need a list of additional mods you have installed

and i think this mob's won't disapwn because i installed this mod after the mod appeared

Yes, the mod will only help with mobs that spawn after youve added the mod