Your saddle position can help immensely in making climbing easier. If you find it a slog at any grade, then try raising the saddle a bit at a time -- say 1cm each time -- and then pedal another good distance. The point that you feel your hips start to rock back and forth with each pedal stroke, then you've gone too far -- back it down a bit just until hips are stable and you're there. Your riding buddy will have fun telling you when your hips are wiggling

The other thing is to make sure your saddle isn't too far back. Try sliding it forward in small increments until you feel efficient pedalling, but not too far that your knees start to hurt. It'll take you a few outings to dial it in, but it's worth it.

What pedals do you have? Are you clipped in? Or on flats? Clipped in is much more efficient, but maybe a bit scary for singletrack if you're not used to them. I ride flats - big platform lugged pedals - in winter because the clips and cleats ice up; but otherwise ride clipped-in the rest of the year (Shimano SPD).

Lugged platforms can be great if you get a good pair - they grip like crazy. These are very good, and not expensive:
https://www.amazon.co.uk/Raceface-PD...ceface+chester

Wear stiff-soled shoes whichever pedals you choose. Makes pedalling more efficient.

Hope this helps...