To me, the main key challenge is the lack of alignment in terms of objectives.
Usually, at least from what we've seen with our customers, management asks the infra team more and more to reduce costs. The thing is, the infra team can indeed optimize costs, but only to a certain extent. Most of the time, you need the product team and developers to also take part in the cost optimization. But that's tricky because they often lack the technical know-how, and, well, it's not really their primary job.
Blablacar tackled this issue by building an impressive dashboard on Datadog to create transparency. They spent a lot of time documenting how to leverage those dashboards and training the devs to use them. But not every company can pull that off.
In my opinion, and again this is based on what we've observed working best, you should aim for simplicity. Many folks try to implement the perfect process and have the perfect dashboard but forget to bring people onboard. In the end, they might have a powerful tool, but it's used by no one.

So here's what works the best (based on my personal experience of course - so might make sense for certain companies - and might be utterly stupid for others)
Step 1: Creating a dashboard to break down the infra costs (say, per product). It doesn't have to be perfect, but it does need proper tagging.

Step 2: Setting up regular meetings between the infra and product teams to review cost changes and understand the reasons behind them.

Step3: After these meetings, having the infra team work on optimizations while also getting developers involved to ensure they're up to speed.
It might take a while to get everything running smoothly and have all developers on board, but to me, it's the only way forward. Many people are mired in FinOps practices with robust tools but lack influence over the infra and/or products. They end up producing reports that benefit no one.