You shouldn’t need display() involved with this and so from the little you’ve provided, I’m not quite following what you are having an issue with.
Beyond that, It is hard to provide you with much feedback on what may work better (or see if it indeed doesn’t work like you may be reporting), or with what versions of software, since your provided code is not a complete minimal reproducible example.
I can point to a complete version of code that works in Voila here to display a plot. You’ll note that display() is not explicitly needed as it is handled by Voila rendering process. Keep in mind though that example is completely unrelated to you and your issues though; it just happened to be something I had handy that involved a plot.
From what you’ve said prior in this post, that approach wouldn’t be testing any of the stuff giving you issues.