edit: gotta be on oreo

install button mapper from your computer to your mibox in the dropdown menu https://play.google.com/store/apps/details?id=flar2.homebutton&hl=en_US (other button mappers might work but this is the one i use)

give it accessibility permission in your system options.

pick which button you want to assign to recents. your choices are home, back (paid), recents (paid-not applicable), volume up/down, headset button (not applicable), add buttons (you can add the dpad buttons: up, down, left, right, and middle ok button.. you can also add the mic button but assigning to that no longer works for long press as of oreo update).

so i picked 'home'. easy to remember. turn on 'customize' after. go to 'long press' and select 'recents'.

now when you press home, it works as usual. when you hold it down, it brings up recents.

https://imgur.com/a/PClsmBa

happy app switching

NOTE: not 100% sure but i think in 6.0 when i installed it, there was a start/stop toggle. now in 8.0, there is a start/stop option in main app menu but doesn't seem to work so i hope the service automatically starts for you first-time users. it's 'on' for me without doing anything but i'm hoping it's not because i turned it on in 6.0 and now there's no way to do it.