I also do fantasy romance, but like an idiot, I create my own 3d models for backgrounds. 0/10, I do not recommend it, it’s way too much effort for something that most readers will skim over.
Depending on what you’re going for, store bought assets should be fine. Yeah people complain when they see sketchup 3d background, but for most purposes they work like a stage in a play, they set the scene and the reader can fill in the blank with their mind. Try not to use them in a way that they attract attention to themselves. Like having what is supposed to be bustling cities be in actuality a ghost town, or a modern cruise ship show up in your turn of the century steampunk drama. You also don’t have to use them all the time. For some scenes, drawing it ‘normally’ can be the best way.
3D assets are tools that can save a lot of work, but just like everything can be misused. But if it is the thing that allows you to focus on the part that is really important for you, go for it. Most of us do this for fun, and the bar for professional use of 3d background is so low, that you’re bound to do better than most