The short explanation
High frequencies fade faster than low ones over a copper run, so a crisp square edge arrives rounded. Equalization boosts the frequencies that suffered most, restoring something the receiver can read cleanly.
It is not amplification. Amplifying a smeared signal gives you a louder smear; equalizing reshapes it.
Where you run into it
This is what allows a device in the middle of a chain to genuinely improve reliability rather than just passing the problem on. Equalize on the way in, re-transmit cleanly on the way out, and each half of the run is easier than the whole.
It has limits. If too much has been lost, there is nothing left to reconstruct.
How the DR HDMI 8K handles it
The DR HDMI 8K applies what the manual calls HDMI Equalevel: precise signal equalization on both the input and the output. Combined with its repeater function that is why placing it mid-run helps, and why it can often replace a separate inline amplifier.
Want to test your own HDMI chain?
The DR HDMI 8K is sold through the HDFury.eu web shop.