I note that in the 2.5 y/o thread you referenced, Manjaro was also installed using only one monitor – reducing the complexity – this is the logical way to achieve the result.
Likewise, in this case, using one monitor to perform the installation of Manjaro makes sense – despite the apparent inconvenience; despite other considerations.
Solve your other issues after Manjaro is installed.
I have seen many threads with similar multiple monitor difficulty, and resolutions seem far ranging. In some cases a new cable may fix an issue; I understand that display port connectors are also considered more reliable.
In some cases a configuration change may help; and those changes are dependent on the hardware in question. Monitor/TV technologies are constantly changing; in some cases a setting changed on the device itself has proven to be a solution.
Again, and in every case, these issues have been solved after successfully installing Manjaro. Another distribution may work out-of-the-box for your specific hardware configuration, or, it may not.
I do not use a multiple monitor configuration, I can’t offer anything beyond that which I have also read in the forums. As I follow those topics (I intend using multiple monitors at a future time), I have noticed that some have immediate success, while others seem to struggle greatly.
However, as you can actually install Manjaro, albeit with only one monitor connected, I suggest a change in the thread title to reflect your actual problem – that your TV/Monitor cannot yet receive signal.
Best regards.
Additionally, please download the latest full Manjaro ISO, to maximise the possibility of success. Cheers.