Your post has been moved to a dedicated topic.
Please provide your full inxi output as described (below) – edit your first post and replace the text there rather than creating another post for it.
You haven’t mentioned how this monitor is connected – via a direct HDMI <=> HDMI cable or an adapter cable of some kind. Have you tried other ports that might be available?
Please provide logs rather than relying on what you might or might not see during boot. If you are unfamiliar with how to generate appropriate logs, manjaro-log-helper might be … helpful.
sudo pacman -S manjaro-log-helper
There is also this tutorial:
Please provide as much detail as you can to help others help you. I’m sure someone will assist when they are able.
Regards.
Welcome to the Manjaro community
As a new or infrequent forum user, please take some time to familiarise yourself with Forum requirements, and the many ways to use the forum to your benefit.
To that end, links are provided (below) - Please use them.
Be prepared to provide outputs from various commands when asked. It’s equally important to provide as much actionable information as possible in your first post, rather than simply indicating there is a problem.
Waiting for others to blindly ask questions can be counter-productive – typically, nobody has a 
at their disposal – Instead, please help others to make informed suggestions, based on information you provide.
Update Announcements
The Update Announcements contain important information and a Known Issues and Solutions section that should generally be checked before posting a request for support.
System Information
While information from *-fetch type apps might be fine for someone wishing to buy your computer, for Support purposes it’s better to ask your system directly; 
Output of the inxi command (with appropriate parameters, and formatted according to forum guidelines) will generate information useful for those wishing to help:
inxi --filter --verbosity=8
or the short form (preferred):
inxi -zv8
- inxi man pages (Arch Manual)