It now listed ARM64 for Linux as an item they work on. This currently number 2 in the feedback user favorites. We are very happy Xojo Inc. finally schedules this feature for implementation. We asked for that long ago.
The feature request 42794 was created in 2016 when Raspberry Pi 3 with 64-bit CPU got available. While most Raspberry Pi computers still work in 32-bit for compatibility, you can run the newer ones with 64-bit Debian Linux distribution. And since Amazon provides ARM based server hardware for their AWS EC2 service, you may enjoy using those machines with Xojo applications soon. AWS with ARM are priced lower compared to Intel based systems. Finally Apple's recent M1 Macs run virtual machines with Linux, which could also benefit from Xojo applications.
For our plugins we have Linux ARM 64-bit support already. All our plugins are built for arm64 and wait here for a future Xojo version to test. Of course we need a newer plugin SDK, which may introduce this target and clarify a few things like the updated plugin structure.
See older blog post Build System Updates for new targets, Building for future Xojo targets and Building plugins for Linux on ARM.
Please know that the roadmap lists various items Xojo Inc. works on, but not all and not necessarily in the order they ship. The listed items tend to be the ones, which takes multiple releases to get finished. Smaller items, which can be done in a few days by an engineer, may not be listed there.