Looks interesting, but after a quick skim it also looks quite simplistic.

What strikes me in particular is how they claim that simple inequalities fix complex theories. Special relativity relies on more than the existence of a limit speed. Quantum mechanics relies on more postulates than just the existence of a minimal exchanged action. In particular, if all those statements were really implying both GR and QFT, how could they be consistent?

The maximal force is something I am not at all familiar with, and that I definitely plan to learn more about when I have the time. From what I understand here, it was long known about general relativity, but has been compared with QFT only recently (the statement “All apparent counter-examples to maximum force disappear when explored in detail” is only justified with papers from last year) so should probably be considered very carefully as an observation about the world.

Another statement that bugs me is the following

The world-wide search for observations beyond general relativity was unsuccess-
ful

Observations at large scale are so incompatible with general relativity that we had to postulate that unknown forms of matter make up most of the universe’s content.

The person that made that paper is a bit out of the mainstream, for what it’s worth. Interpret as you wish, doesn’t mean they’re wrong, but y’know…