Chomp is still pretty ass, scale shot isn't even the best set let alone saving it.
First of all,
Fairies. Clefable, Enamorus, Hatterene, Iron Valiant, Ninetales-A and Ribombee in addition to some terastalizers such as Iron Moth and Kingambit.
All Fairies: Deny scale shot, making Garchomp super easy to revenge kill

With unaware, physdef Clefable can 1v1 all Garchomp and use it as setup fodder for calm mind/cosmic power. Even if not setup variant, clef can get up rocks and force garchomp (without a speed boost) to prematurely terastalize just to not die to moonblast or get forced out.

Not only is it immune to scale shot, but also Earthquake. Only options for actually threatening Enamorus are Tera Blast which has high opportunity cost especially on a bad mon and Stone Edge which leaves you stonewalled by Corviknight and Gholdengo with air balloon intact (more on them later). Enamorus also outspeeds and, once again, forces premature tera or a hard swapout.

Possibly the least big problem for scale shot Garchomp, unless it's seed Hatterene on gterrain. Completely messes up utility Garchomp but this post isn't about that.

Moving on from the least big problem, we have the most problematic for Garchomp. Iron Valiant has a very high usage rate, booster quark drive to revenge kill even +1 speed Garchomp, fast encore to punish scale shot and swords dance, again forces Garchomp to tera. If Garchomp has already terastalized before Valiant comes in it's even bigger Valiant food because it can't even tera to resist moonblast if it gets lucky enough to even setup in the first place vs a competent player.

Fast encore, aurora veil, snow defense boost, it's debatably as bad of a matchup as Iron Valiant but it's less common. Ninetales is still a significant, noteworthy threat though.

Generally gets sacced early game, however Webs nullify scale shot even if Ribombee is taken down.

Iron Moth can punish Garchomp for terastalizing because Garchomp is usually the teams Moth check, take away Garchomps typing and it fails to answer Moth. Moth can also emergency tera fairy if it needs to block scale shot speed boost.

Kowtow has a chance to OHKO without glasses or tera at 3 fallen +0. Kingambit eats EQ after tera. No elaboration needed because Kingambit revenges every threat.
Next,
walls.

Garchomp isn't doing shit to Dondozo, it's just curse setup fodder.

Ting Lu has very similar physical bulk to Dondozo but trades curse and unaware for spiking and phazing Garchomp out. Garchomp will win over time but when Garchomp finds so much difficulty setting up 1 phaze is all you need to neutralize Garchomp.

Running stone edge to even touch Enamorus? Well now you can't touch Corviknight at all

Needs air balloon intact or terastal, but can easily take on weakened Garchomp if not running fire move
Miscellaneous Counterplay not mentioned earlier:

Grassy Terrain halves the threat of Earthquake, Grassy Glide can do decent damage and goes before even +6 speed chomp.

Bulk up variants can set up alongside Garchomp, have Ice Spinner and Earthquake/Headlong Rush if Garchomp teras.

Rain and Sun have powerful pokemon with speed boosting abilities that threaten Garchomp with ease such as Walking Wake, Barraskewda, Roaring Moon and Basculegion

Dragonite has tera normal + Extreme Speed alongside Multiscale to 1v1 Garchomp
What should you
use over Scale Shot Garchomp though?

Outclasses Garchomp as a Ground type sweeper

Outclass Garchomp as Dragon type sweepers

Outclass Garchomp in the role of sweeper that checks Iron Moth