I would say look into the following devices and if you want just Manjaro then best is to flash Mainline uboot with Manjaro image over emmc.
Amlogic S922x Soc’s ( Panfrost GPU support might be available from 5.10)
Beelink GT King Pro - TV Box but have good Manjaro Image maintained by me and currently posting from it.
Odroid N2+ (If you can purchase locally else internaltional shipping is too high)
RK3399 Soc’s ( already have GPU support while VPU will be available in 5.11)
4. Radxa RockPi4C
5. Firefly Station P1
6. Pine64 RockPro64
With these you can easily compare it with Intel Atom mini pc devices. All the boards mentioned have very good Manjaro Arm Image.
If you need it for video playback then you will have to wait for VPU support on Manjaro and for light gaming currently only retro games are working well with Panfrost on RK3399.
Finally it would be best for you to go with X86 mini pc’s, BTW Beelink will be launching some Manjaro Pre-installed Mini Pc’s Like Beelink GTR (High end), Beelink U55, U57 and maybe lower end model too.