Hey Abi! Thanks for passing by (and for this first comment to my post)!

So, gamma-rays are only considered to be a byproduct of WIMP annihilation if they are undetectable, and, therefore, possible to exclude from data?

There are many ways to generate gamma rays in the universe. Dark matter annihilation is one of them.

The point here is that when induced by WIMP annihilation, gamma-ray production has specific properties that could be observed. But we have not observed them. Consequently, such a production mechanism can only occur with a tiny suppressed rate (connected to the y-axis of the last figure).

To rephrase what I said::

1. Primordial black hole could be dark matter, but under the condition that we have a second dark matter particle.
2. We assume that this second dark matter particle is a WIMP.
3. In this case, it has been demonstrated that WIMPs generate many special gamma rays that should have been observed.
4. We didn't observe those gamma rays.
5. If WIMP and back hole dark matter coexist, then we have huge constraints on WIMPs as they would generate something unobserved. In other words, the value of the parameter displayed on the y-axis of the last figure has to be small enough to suppress this gamma ray production.

is it clearer?