G'day
@SuperuserRoot and welcome to linux.org, albeit under difficult circumstances
I have just been watching up until now, as I have every confidence in my friends above, but I will throw in my two cents worth now. Some of the following are comments/tips, and some are questions you might be able to answer for us.
1. Question - Has this laptop had Windows on it before and if so which ... and do you have a Windows bootable medium available to test with?
2. Question - What is the brand name and model number of the laptop? It may be the case that a search will reveal similar problems with that model (solved or unsolved).
3. Comment - with regard to
If previously you had had the BIOS set up to boot from bootable USB stick (if present) first each time, then you would simply boot up, without having to use Function or Escape key combinations.
I have my secondary rig, a Toshiba Satellite, set up in this fashion, works every time, and the day it doesn't will be because it needs repairs.
4. Question - Which DE (Desktop Environment) version of Manjaro.
5. Comment - on the basis of how you go here, it is a good investment to have a bootable USB stick with Timeshift on it. Does not solve all problems, but can fix many.
Cheers and good luck
Chris Turner
wizardfromoz