when can you make a 1.12.2 supported mod?

Uh why would you want to make a mod that uses architectury on 1.12.2 if fabric exists for 1.14+ only?

Also why do you want to play on minecraft 1.12.2 in the first place, 1.16 and 1.17 are the latest versions

https://legacyfabric.net/

i need it for forge

Architectury only supports 1.15 and up, with 1.16 and 1.17 being the currently active versions (AFAIK).

Backporting is extremely unlikely, especially considering Fabric is pretty much nonexistent (officially) on earlier versions.

wagyourtail I meant the official fabric, not a fork

yeah. well legacyfabric is the only one and is as "official" as it gets for <1.14, their quality and dedication is on par with fabric.
As for actually making arch-api for older versions, it's not worth the time to support older minecraft versions anyway.

We support 1.14+ with the current toolchain, and has no concrete plans to support the more legacy versions, Architectury Loom for 1.12 might happen, but the various Forge Gradle forks may get you that anyways. Legacy Fabric is incomplete and has severe problems (Sorry people from there I know I abandoned you all), and isn't on the list of viable mod loaders to support, so developing multiple mod loaders for versions before 1.14 is pointless.