Life Mage's Apotheosis doesn't work with Ectoplasmic Slime's Concoction

PC, v 023.5. The buffs gained from healing aren’t shared to the rest of the team.

I just realised, is this because the slime specifies it has to be ‘another creature?’ I guess that would make sense. Kind of annoying though.

Exactly.

Same with with Glutinous Slime and Conquest spell gem. Because the stat bonus from Conquest comes from nowhere it isn’t shared by Slime’s Abomination trait.

You could try Ancient Spirit maybe this triggers Concoction.