Indeed Retromat is very inspirational for spicing up the Retrospectives for your developers. But at some point I faced the same issue of minor effectiveness in my team -after one year of working together, after 20 retros .. - so I started as well to think about some solutions to get higher again the attention level.
Discussion was going not really somewhere so I thought to point out a Retrospective Topic.
Now I prepare the team, before the Retro, with a couple of Topics to discuss, maybe some issues we had, or some improvements that I see that are needed, but also the team can come up with topics. Plus I also leave the total freedom to improvise topics directly during Retro. That helped a lot to give new energies to the people.