I worked with both engines and to give my humble opinion, it hugely depends on the project if Unity or Unreal is better suited.
For saving you time I won't mention obvious advantages, you all probably know them anyway, but
to pointing at the elephant in the room,
under the right circumstances weaknesses become strengths and vice versa.
The mobile market ist dominated by unity!
One reason for this is the still wide usage of "stoneage calculator" phones. With version 4.25 unreal stopped the support for my phone (guess I'm old). Further to be successful on the market, the app installer has to be as small as possible (otherwise user won't even bother to download and test your app). An Unity build is far smaller than an Unreal, therefore better.
Comparing both Communities, Unity has a lot of people "knowing how to build paper planes", fundamentally they know how to build an aircraft, yet in Unreal you find the aeronautic pioneers trying to figure out space travel. One year in the unreal community taught me more than 8 years in unity. Explains the difference in quality of the marketplace
If you recruit, you will find a lot of talented unity developers for a copper, compared to an average unreal developer costing a gold coin.
Blueprints in Unreal are fantastic, but at one point you have to go deep into C++ to solve your problem. Unreal gives you its source code, that's pretty huge (unity requires reflection hacks), but its overwhelming and at times pretty slow. If I make a small mistake, I have to compile 5 minutes to notice my error. In C++ I need 1 week for something I do in C# in 1 day. Time is money and your team will be faster with unity.
Games that require "crazy game play" will also benefit from Unity. An example is Unity's DOTs, perfect for a simulation game. Unreal is not suited for that kind of game. A successful indie game either has "a unique artstyle to die for" or "creative gameplay".
Investors and publishers will take you more serious with Unreal, that's a sad fact, but a good game project will stand out anyway.
I have to pay royalties, isn't engine X better than Y?! Forget this mentality, because if you really reach that phase with your project, it won't determine your financial success
I could babble a lot more, but my point is,
there is not clear winner in unity vs unreal.
Personally, I prefer UNREAL, because as a shader programmer, I really started to hate Unity's render pipeline..... each new unity version fucks up your old code and hope their engine team figures out, which render path they actually like to follow. Unity has a tiresome tendency to try new gimmicks without delivering (a lot of plugins simply disappear), while Unreal so far delivers. A good example is the Control Rig, it's not perfect, but with each version it gets better.
Nanite and Lumen aren't perfect. Worse, it's a bad rookie mistake to use them to solidify your argumentation ... please don't be angry, I tell you why!
In practice Nanite can only be used in a stone or city environment, because there is no vertex displacement. Therefore no vegetation, no wind, no characters. Even worse, imagine a world, where everything is so perfectly detailed, except your main character, because.... well nanite doesn't support skinned meshes. Nanite might be awesome, but it requires "modern" hardware, so only a small percentage of players has the required hardware.
Lumen has the obvious problem of .... I can achieve the same effect with precalculated lightmaps and my players don't need an RTX Graphic Card or better. The number of applications for realtime lightning is slime, day-and-night cycle, maybe a latern in a dark cave.
Don't get me wrong, I'm excited for those new technologies! Game Development is like being a wizard, you need to kill a bug, why bother using fireball if firebolt works fine, without risking to set everyone in flames.