Do not break the bolt if possible.
Can you tell:
Is it possible to turn the washer and/or cup spring below the bolt’s head by hand?
Try that with the bike laying on the left side.
While you try to turn the parts with one hand, use the other hand to pull the right crank gently upwards and downwards - crank in 90° position related to bottom tube (to generate torsion of the bottom tube).