I'm running out of ideas because I can't find anything useful of any of the messages from your dmesg. Can you try booting Manjaro with the opensource boot option but before you boot edit the boot options and then remove the following options from the line that size linux and then press ctrl+x to boot.
The only thing errors I find in your dmesg are these but I can't find anything about them.
Code:
driver=free nouvea.modset=1 i915.modeset=1 radeon.modeset=1
[ 57.844648] [drm:amdgpu_dm_atomic_commit_tail [amdgpu]] *ERROR* Waiting for fences timed out!
[ 63.374471] [drm:amdgpu_job_timedout [amdgpu]] *ERROR* ring gfx timeout, signaled seq=362, emitted seq=364
[ 63.374521] [drm:amdgpu_job_timedout [amdgpu]] *ERROR* Process information: process gnome-shell pid 1788 thread gnome-shel:cs0 pid 1818
[ 68.965972] amdgpu: [powerplay] Failed message: 0x28, input parameter: 0x500a8, error code: 0x0
[ 72.148359] amdgpu: [powerplay] Failed message: 0x26, input parameter: 0x4012c, error code: 0x0
[ 75.323564] amdgpu: [powerplay] Failed message: 0x28, input parameter: 0x60000, error code: 0x0
[ 78.508722] amdgpu: [powerplay] Failed message: 0x27, input parameter: 0x503, error code: 0x0
[ 81.683051] amdgpu: [powerplay] Failed message: 0x27, input parameter: 0x502e4, error code: 0x0
[ 84.859487] amdgpu: [powerplay] Failed message: 0x27, input parameter: 0x40320, error code: 0x0
[ 98.084632] [drm:amdgpu_dm_atomic_commit_tail [amdgpu]] *ERROR* Waiting for fences timed out!
[ 103.694467] [drm:amdgpu_job_timedout [amdgpu]] *ERROR* ring gfx timeout, signaled seq=602, emitted seq=603
[ 103.694520] [drm:amdgpu_job_timedout [amdgpu]] *ERROR* Process information: process gnome-shell pid 2679 thread gnome-shel:cs0 pid 2708