I'm not sure why, but for my level 1 animal enhancement for my Simic Hybrid character, I am unable to select Nimble Climber. I am trying from the website not the app, and I think I was able to choose that enhancement at first, but now it doesn't show up as an option. 
For now, I will continue in my campaign as if my character had Nimble Climbing (I'll just tell my DM my climbing speed is equal to my walking speed), but it's a bit frustrating that I can't select it for my character digitally. 

Please post the url to your character sheet so someone can take a look.

I wonder if the system somehow has you already *having* Nimble Climbing? Try setting the Animal Enhancement selection to -- then go to a different page, then go back, then see if it shows up in the selection dropdown.

Edit: You may need to repeat that process once or twice.

So I tested and works perfectly.

Choose Simic race. Under animal enhancement, scroll to bottom, and select Nimble Climber.

What do you see what you try this, can you screen-shot it?

character sheet: https://www.dndbeyond.com/profile/colllllllins7/characters/58524625 

But actually, in my character sheet, strangely enough, under Animal Enhancement, it says "No Choice Made" but then Nimble Climber, so maybe the system's just being buggy. 

It might be saying that in expectance of a choice to be made at 5th level.

Anyway, it has been selected and if you click your Speed, the climbing speed is applying. So, all good.