When we talk about more work efficiency then which is more recommended. ? An ultrawide monitor or a dual monitor? Which have you found to be most beneficial to your work environment and why?

If you had the option to switch to the other, would you?
I prefer dual monitor myself as for I can have a window snapped to that SCREEN ( full screen to that screen ) that is independent of the other display. Otherwise everything needs to be windowed and placed and sized.Ultrawide monitors are more productive monitors as compared to dual screen monitors setup. Ultrawide monitors have both PRACTICAL and aesthetic advantages over the dual monitors and helps you a lot to overcome challenges.Here I found one reference ARTICLE for you.
https://thebestmonitors.com/ultrawide-vs-dual-monitors/I'd rather have a Dual Monitor setup than an Ultrawide.

Ultrawide may PROVIDE some benefits in certain games that support it. However, games that don't properly support it are going to look pretty terrible, depending on if the monitor letterboxes lower resolutions.

However since it is one monitor, most games are going to completely monopolize the screen. Conversely, it is possible with a Dual Monitor setup to have a game on one monitor in full-screen while watching Videos with another.

I've never bought the "productivity" argument for ultrawide monitors either, certainly not compared to dual monitors. I don't know how much benefit it provides for video EDITING but that hardly eccompasses productivity tasks.

IMO having two separate screenspaces is better than having one double-wide screenspace.