nektos/act

Hey guys, I'm having some trouble with ::set-output, maybe one of you guys can spot what I'm doing wrong?
I'm trying to turn the contents of a file into an output from an action, but nothing I do seems to work. (According to the internet this should be fairly simple)

Here's my (debug) yml (with debug probes):

    - shell: bash
      name: Retrieve Binary Path
      id: retrievebinarypath
      run: |
        PATH=$(cat $HOME/binaries.txt)
        echo "Path is $PATH"
        echo "BINPATH=$PATH" >> $GITHUB_ENV
        echo strawberry
        echo ::set-output name=binarypath::$PATH
        echo ::set-output name=altbinarypath::${{ env.BINPATH }}

    - shell: bash
      name:  Display binary path to user
      run: |
        echo "From Steps: ${{ steps.retrievebinarypath.outputs.binarypath }}"
        echo "From Steps (alt): ${{ steps.retrievebinarypath.outputs.altbinarypath }}"
        echo "From ENV: ${{ env.BINPATH }}"
        echo "From Outputs: ${{ outputs.binarypath.value }}"

and here's the output I'm getting from act:

| Path is /tmp/arduino_build_688801/Device.ino.elf
| strawberry
[Verify Devices/verify-devices-2]   ⚙  ::set-output:: binarypath=/tmp/arduino_build_688801/Device.ino.elf
[Verify Devices/verify-devices-2]   ⚙  ::set-output:: altbinarypath=
time="2022-01-22T21:36:18+01:00" level=debug msg="Wrote command '\necho \"From Steps: \"\necho \"From Steps (alt): \"\necho \"From ENV: \"\necho \"From Outputs: \"\n\n' to 'workflow/composite-3.sh'"
time="2022-01-22T21:36:18+01:00" level=debug msg="Writing entry to tarball workflow/composite-3.sh len:86"
[Verify Devices/verify-devices-2] Extracting content to '/mnt/g/Projects/HardwareMonitor'
[Verify Devices/verify-devices-2]   🐳  docker exec cmd=[bash --noprofile --norc -e -o pipefail /mnt/g/Projects/HardwareMonitor/workflow/composite-3.sh] user= workdir=
[Verify Devices/verify-devices-2] Exec command '[bash --noprofile --norc -e -o pipefail /mnt/g/Projects/HardwareMonitor/workflow/composite-3.sh]'
[Verify Devices/verify-devices-2] Working directory '/mnt/g/Projects/HardwareMonitor'
| From Steps:
| From Steps (alt):
| From ENV:
| From Outputs: