It's not (not even if you count associated phenomena like ocean acidification). But everything else is small potatoes in comparison, mostly because markets are adequate to find compensatory approaches for most of them.

Just so you know, my 10C worst-case-scenario comes from https://www.nature.com/articles/nclimate3036, before which I'd expect to see global climate engineering (but social upheaval might prevent us from effectively enacting the measures...but then again, the same upheaval would also prevent carbon store exploitation to that extent), but anyway it renders latitudes up to ~30 degrees plausibly uninhabitable and of limited use for robotic farming, but enabling season-wide use of >60 degrees latitude, for an overall decrease of plausibly human-exploitable land by about one-third (handy land area histogram: https://www.researchgate.net/figure/Landmass-distribution-by-latitude-Southern-and-northern-landmasses-are-added_fig1_224798944). Of course, 10C is double the IPCC's worst-case scenario, which itself is double its most likely scenario.

It's also worth noting that we spend only ~5% of GDP on food production, which is the most critical thing to invest in to avoid massive population collapse, so we have a lot of headroom there.

Equatorial-to-polar ocean currents transport massive amounts of plankton with different temperature tolerances all the time, so losing the majority of the photosynthetic capacity of the oceans is unlikely (and again, biogeoengineering is possible there), etc. etc. etc..

Mineral resource depletion can be tackled to a significant extent by landfill mining (https://web.mit.edu/12.000/www/m2016/finalwebsite/solutions/landfill.html); yes, it's more expensive, but again, we have headroom for the critical applications and the non-critical ones...well...we won't die.

Ecosystem degradation (including topsoil loss) is a huge problem, but as long as we avoid outright desertification, a lot of ecosystems rejuvenate substantially once we stop brutalizing them (e.g. much of the "wild" area in the northeastern U.S. is former cropland). This isn't universally true, and for any ecosystem that creates its own climate (e.g. Amazon) you can pass extremely-difficult-to-reverse tipping points, and of course species can go extinct (and we don't know what the minimum viable population is for most species), but...we won't die. And once we leave somewhere alone, a lot of it will recover to an extent (maybe a rather sad extent, but not a life-threatening lack of one).

And so forth and so on it goes throughout the numerous immense challenges we're creating for ourselves. Even all at once, when you account for how adaptable humans actually are, when you examine the kinds of conditions we manage to live in, and the willingness we have to shape our environment when we need to to survive, it's really hard to find a scenario wherein the carrying capacity of the planet wouldn't be in the billions for arbitrarily far into the future, or wherein we would inadvertently end up far below the planet's carrying capacity.

Save for some sort of planetary-scale superdisaster like global thermonuclear war, we're too capable now to be reduced to hundreds of millions. We might ravage the planet to an extent that would make our current attitude look like we're positively beneficent custodians. But unless we decide (or market dynamics "decides") that the target population is hundreds of millions, the gradual stuff we're doing won't result in us ending up there. Feel free to mention details, but almost all the predictions of catastrophe fail to distinguish between sigmoids and exponentials, and/or make completely historically-unrealistic assumptions about which constraints are fixed and which are malleable. (And that's without even taking into account the unpredictably transformative nature of technological innovation.)