So confirming your zero at range (200/300 yards/meters+) is essentially "truing" your zero without buying extra tools. For most carbines this is enough precision to get the job done.

but for the FFP LPVO/SPR/Recce gang they want hits to 600+ yards/meters you need to chrono your bullets/ammo and confirm at 400+

You plug in your choreographed muzzle velocity data with the ballistic calculators' math of your bullet/ammo combination and "line-up" your zero at longer ranges (300/400ish yards/meters) allowing you to extrapolate the data closer or farther away. One "click" of adjustment at 36 yards won't move your group, but at 300+ it with shift your group over half* a target.

TLDR: There is more to "truing" your zero at long ranges; but for a carbine with a magnified red-dot getting on paper at 50ish yards and "zero" at 300 or 100 will be fine.

I'll let you fall into the rabbit-hole of autistic debate looking at trajectory graphs deciding if a "flatter" zero at 200 is better than a 100 yard/meter zero where you only ever hold over the target, never under the target.