Which Archicad version are you using? Archicad 23 introduced multi-segment Columns and Beam using which you should be able to model those Beam ends.
I see - sorry!
correct me, but the beams in the slab "in real live" should carry the slab - and should reach ( lay on ) the surrounding wall-forms, so they shouldnt connect to the slab but "lay on the wall" instead?
What you could do in every such situation - not using beams but unsing morphs, which you could easily cut off at any angle