Do they affect climbing?

I can see the obvious benefit from having your weight further back, but are there other benefits?

I found that moving from a 90mm to a 70mm on the Blur made tight corners a bit easier.

I have a 50mm stem on my Heckler…

Doesn't hamper me ( pushing 😳 ) uphill…

Shorter stem moves your weight further back on the bike. Which *can* affect climbing…

*it doesn't always though, depends on too many more variables than just the stem length to be fair, including seated Vs standing whilst climbing, how smooth a pedaller you are, whether you spin or mash etc.

Makes it easier to get round uphill switchbacks as above. Otherwise, no real issues tbh

Speeds up the steering, which compensates a bit for everything else slowing it down – wide bars, slack forks, fat tyres.

Definately makes a difference on what you could call careless climbing… You can get your weight forward easily but it's still slightly more involved than just sitting on the bike like a sack of spuds.

Shorter stem puts your weight slightly further back. Depending upon other factors (saddle position relative to bars, weight relative to rear axle, length of stays etc etc) you might find the front end gets light and wandery earlier than with a longer stem when climbing.
If you can still get up your steepest climb, then it isn't too short!