The current version of Acorn (v6.6.2) is fully compatible with MacOS 11 Big Sur on Intel. We're about ready to release version 6.6.3 which fixes some cosmetic issues with MacOS 11, so look for that in the coming days.
A universal binary of Acorn for Apple Silicon is taking a bit longer than I originally planned (2020 is the gift that keeps on giving for us). For the most part, Acorn 6.6.3 runs fine in Rosetta (the translation layer that the new ARM based Macs use to run non-native Mac apps).
However a couple of the tools* aren't compatible with Rosetta, so we've had to do a complete rewrite for those.
Update: Apparently these tools decided to magically start working again in the latest Big Sur release. I'm not sure how or why, but- hey, thanks Apple for fixing that.
The good news is I took a fresh look at those tool backends when rebuilding it, and I'm happy to say the newer versions are quite a bit faster.
The plan is to have a public beta of a Universal Binary of Acorn in the near future, so if you have one of the new Apple Silicon based Macs you'll be able to kick the tires on it at full speed.
You can download an Apple Silicon ready Universal Binary for Retrobatch right now. This beta version (v1.4.3) is fully compatible with MacOS 11 Big Sur as well. We hope to have the final release ready in a few days.
Apple Silicon Mac Thoughts
I'm pretty excited about the new Apple Silicon Macs. I've been developing on one for a number of months now, and I'm very happy with a number of aspects of it, most especially the shared memory between the CPU and the GPU. This has enabled various tools (such as brushes) to speed up dramatically in Acorn, without me having to do anything to support it. It's been pretty great.
* The specific tools we had to rewrite for Acorn are Flood Fill, Instant Alpha, and Magic Wand selection. These tools were originally written in OpenCL targeting the CPU, which unfortunately isn't supported in Rosetta. Update: Maybe they are now shoved through a compatibility layer, and sacrifice speed for working?