We are using dw20 1.19.2 v 1.2.1 and it appears that items will generate but bosses refuse to spawn, no lightning, no color bars above head, the only boss Ive found is a Hoglin in the nether. The bosses refuse to spawn in the end and in the overworld

Boss generation settings are very configurable. Consult with the modpack author, as you have not described anything that could not be achieved through configuration.