Product: Synergy (all versions)
Operating system: Linux
Synergy 1
When downloading Synergy for Raspberry Pi, you'll need to choose between ARMHF and ARM64. If you're unfamiliar with what "ARMHF" and "ARM64" mean, see the background section below.
Synergy 3
There are currently two types of installers available for Raspberry Pi hardware, a Raspberry Pi OS installer, and an ARM flatpak for other Linux operating systems.
After downloading you will be given a command you can copy to install Synergy via the terminal.
All Synergy 3 installers are only supported on ARM64 (64-bit), if you have an older Raspberry Pi with 32-bit hardware, you would need to use the ARMHF installer from Synergy 1
Background
ARMHF stands for "ARM hard float", and is the name given to a Debian port for ARM processors (armv7+) that have hardware floating point support, which is found on most modern 32-bit ARM boards. ARM64 (also known as AArch64) is the 64-bit extension of the ARM architecture. Raspberry Pi unveiled the beta of its 64-bit version of its Debian-based OS alongside its then new 8GB Raspberry Pi 4 in mid-2020, and is now gradually becoming more commonplace.
In short, ARMHF is 32-bit, and ARM64 is 64-bit. You'll need to install the right version for your Raspberry Pi OS (formerly Raspbian).
How do you know whether you're using the 32-bit or 64-bit version of Raspberry Pi OS or Raspbian?
If you have a Raspberry Pi 4, then you may have installed the 64-bit version of Raspberry Pi OS.
However, rather than guessing, there are a few commands you can run to find this out:
sudo apt install lshwsudo lshw | head -6
The value of width indicates 32 or 64 (meaning 32-bit and 64-bit respectively).