You're confusing an approved technique with an authorized use of that technique. Yes, Minneapolis police policy permitted certain neck restraints in 2020, but that didn't give officers unlimited authority to use them.
MPD policy also required force to be reasonable and proportionate, and officers were trained to move restrained suspects into a recovery position to prevent positional asphyxia.
Floyd was handcuffed, face down, and restrained by multiple officers. Chauvin continued applying pressure for over nine minutes, including after Floyd became unresponsive and stopped breathing.
The police chief and multiple MPD training officers testified that Chauvin's actions violated department policy. The Minnesota Court of Appeals subsequently upheld his conviction.
And what exactly does swallowing narcotics have to do with continuing to restrain someone after they're unconscious? Preventing the destruction of evidence doesn't justify lethal force against someone who no longer poses a threat.
The existence of an approved restraint technique was never the central issue. The issue was whether Chauvin's particular use of force was justified. The evidence and the courts concluded it wasn't.