That is to say: It should not be a herculean effort to create an adoptopenjdk release that runs on M1s natively, so presumably, it will happen.

So: It's not there yet, but note that JDKs for ARM have been available for more than decade, and whilst JDK 15 has dropped support for a bunch of exotic OS/architecture combinations (such as Solaris), ARM development has always remained at least partially relevant (even if so far it's mostly an Oracle commercial license offering). That (probably) won't run on macOS on M1 hardware, but that's 95% of the work already done. If you instead leave Operation System on 'any', you'll note aarch64 is in there, and this gets you to a Linux release for ARM processors. Possibly, as Apple no doubt has a bunch of extensions built into their M1 designs, and Apple gets its own.

On this page: AdoptOpenJDK Latest Releases you can select 'macOS' from the 'Operating System' dropdown, and then from 'Architecture', it's currently only 圆4, but soonish there should be AArch64 or ARM64 (those are usually the shortcodes for 64-bit ARM).

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