Co-creator of Voila here. Voila is rather un-opinionated about what you can run in it. While it offers excellent support for ipywidgets, it's certainly not confined to that. One downside of Voila is that it can be resource-intensive, as it creates a new kernel/process for each page view or browser tab.
Mercury, in my view, seems really interesting for quick demos and reports. It's somewhat akin to Streamlit, making it ideal for notebook authors.
On the other end of the spectrum (and pardon my shameless plug here), there's Solara (https://github.com/widgetti/solara/). Solara is a fully-fledged web framework for Python, specifically designed to handle app sizes that surpass what Streamlit and Dash can manage. It's worth noting that Solara can render ipywidgets, using a pure Python React-like framework. This can be particularly useful after the exploration phase, when you're looking to transition a project from the notebook into production.