This category is used for agents, mixtures and exposure circumstances for which there is limited evidence of carcinogenicity in humans and less than sufficient evidence of carcinogenicity in experimental animals. It may also be used when there is inadequate evidence of carcinogenicity in humans but there is sufficient evidence of carcinogenicity in experimental animals.

[...]

This list is focusing on the hazard linked to the agents. This means that the carcinogenic agents are capable of causing cancer, but this does not take their risk into account, which is the probability of causing a cancer given the level of exposure to this carcinogenic agent.

https://monographs.iarc.who.int/wp-content/uploads/2018/06/CurrentPreamble.pdf

The results in this case were deemed limited by the IARC, meaning:

[...] chance, bias or confounding could not be ruled out with reasonable confidence.

https://www.iarc.who.int/wp-content/uploads/2018/07/pr208_E.pdf

Seems to me like one should expect more concrete evidence after decades of active research on the topic.

https://www.bbc.com/future/article/20230630-aspartame-what-else-is-possibly-cancerous

A practically worthless designation.

Yes, but the term radiation usually implies ionizing radiation.

My understanding of Group 2B is that it's assigned to whatever IARC researchers get enough lobby money for to classify in some way. They'll give some lab rats a gargantuan dose of the substance, something will happen, and 2B can be assigned.

Put another way, they found all the Group 1 definite carcinogens by the early 2000s and needed a reason to keep researching after that. Of course there are some new substances that pop up regularly that need to be investigated but beyond that there's a significant established base of knowledge.

With the RF specifically its interesting that some groups have correlated it to negative health outcomes, but nobody as of yet has shown how it can even affect the human body, let alone cause cancer.