Sadly, I don’t think so. Searching about that I found out they switched to GTK3 interface being default just before GTK4 was released… And making the switch from GTK2 took a long time.

I admit for the very limited things I do and only occasionally I use Paint.net

Still in my mind Gimp is much more powerful?

What’s the difference with using custom tabs? It already allows you to open link without leaving app. If it is mainly about browsing history I guess you wouldn’t want to have history no matter which app you used and so you could set custom tabs to open in private mode by default. (At least you can with Firefox)