I think I am hardlocked
I can no longer progress, cannot kill the current enemy and improve / upgrade anything.
I cannot reach level 100 for rebirth and Ascension no longer seems to provide a
way to reset the current stage?
Ascension always provides a way to reset, you just hit the ascend button on the combat section. You need to be a high enough stage but the requirement never changes.
Getting to level 100 for rebirthing requires a mix of equipment tiers, souls, max level perk in tree & the ascension upgrade for max level.