Training for very steep climbs on the mountain bike

Hi everyone. I have a slightly different challenge: I have fitness to climb local 15-20% grade climbs. However, when terrain becomes technical with ruts, roots, rocks, I find it hard to navigate. My shoulders tense up, and sometimes I have to dismount, or topple over.

What can help me stay on course during long steep climbs? Balance skills? Core strength? Unweighing hands? More aerobic fitness?

I am new to mtb, still learning basic skills such as trackstand and bunnyhop…

Thank you.