This isn't my field but I was curious and found this paper that, in part, says:

"Although Mair and Hornig’s ν14 frequency assignment of 1310 cm−1 has been widely accepted, it has become a great puzzling problem for the theoretical researchers because no advanced quantum chemistry method has realized its rigorous calculation so far (see Supplementary Table 1)."

Wang, S. Intrinsic molecular vibration and rigorous vibrational assignment of benzene by first-principles molecular dynamics. Sci Rep 10, 17875 (2020). https://doi.org/10.1038/s41598-020-74872-6

Dear John, many thanks to you for your constructive and prompt response! We are now all curious, especially because the vibration is visible in the nanocoating, which may have an interesting application as quantum material.

Hi Jan, my guess is that the complex does no longer have the D6h symmetry of Benzene. Once the symmetry is lowered, additional vibrations become IR- or Raman-active - for the lowest symmetries there is no longer the mutual exclusion role and all vibrations are IR- and Raman-active...

Dear Thomas, thank you for the explanation, which I find clear and understandable. However, I would then be interested to know whether there is another fundamental vibration of benzene (e.g., specific to a higher degree of symmetry) that disappears in this situation, or shifts, thereby indicating a reduction in symmetry in favor of the vibration at 1310?

Dear Jan, chances are that there is, but one would need to know the symmetry of the complex. In addition, in benzene's IR spectrum there are more than the 4 bands one would expect due to symmetry considerations because of higher harmonics (which are stronger than expected because of Fermi resonance...).