Edit: Ah, simulate, not emulate... But OpenWRT is likely best bet, if it exist, its there or somebody knows from wifi mesh networks, routing technologies with 5G router support. Git logs and developer commits should all else fail, if not their design they would know about the specifications and standards implemented. And the 5G/6G focus might be misleading, as network topology and routing just ned tunable latency, bandwidth, and link quality and maybe networking-planning frameworks that fits the purpose exist, that allow for larger test cases. But important enough to likely exist nearline hardware and firmware researchand development.

I think the usual suspects here would be OpenWRT, Alpine Linux and other usual suspects for preferred distrobutions for such things. Additonally, if there is anything in mainline Linux kernel, i.e. modules and test frameworks more nearline hardware/infrastructure for basic functionality testing. RabbitMQ community as popular in telecom may also be a route to ask this. As soon as you have distributed logging and/or network traffic generators and testers... Doubt it is easily found around more high level frameworks for logging and analysis.

Edit2: Almost certain to exist, and likely open for industry support of open source if shareable frameworks with broad application doesn't exist. But something that possibly should exist with Hardware-In-Line simulationa and functionality. HIL is a buzzword I've been surprised haven't been a concept and hook around HPC in the past, but given industry applications, not in academia and open source as much, with it's aviation history and an engineering topic. So if academia makes a framework, industry would use and support to for shorter time to products with new netwokring technology. Maybe someone even have a guy with a master degree that can be made a professor and write an unsupervised PhD and become associate Professor if there is a chicken and egg problem between industry and education. Whatever anyone does here, it must work with current market products and competitors.

Shouldn't be a choice here between telecom and semiconductor industry, and a difficult thing to spearhead and maintain open source trust from negotiation about show and tell? It has to exist, too much cost and time involved. If not a collection of naive test beds, and not really something that get made from individual community efforts unless added to broader and more basic scopes, down to virtual machines and kernel facilities.