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is this a problem? do you for example have high GPU usage but low FPS?

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Resolution?

I had a 3060 Ti and did mostly max out GPU usage in NMS at 1440p - my current 6750XT does the same (85 to 100% usage) at max settings, especially if resolution scale is increased a bit, so I'd say this is intended. If you have no performance issues, it's nothing to be concerned about.

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Welcome to the future where many games use more computer resources during pause or the main menu than actually playing the game.

Are you sure you are monitoring the 3D engine load? How are you monitoring the 90% load, through Windows task manager?
Some games use the 3D engine and Video engine as well, but No Mans Sky doesn't look like one. Depending on the monitoring software, sometimes doesn't take in account the lower clock to save power.
A simple (and powerfull) software like GPU-Z or HWinfo has all the monitoring tools you need, take a look at "Power Consumption %", this will tell you if you are really using the 90% load on the card.

No Man's Sky does a huge amount of procedural generation, the GPU is much faster at generating noise (the basis for most Procgen) than the CPU, so I wouldn't be surprised if that was why you are seeing high GPU usage.

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As suggested by Dark_art_, you can indeed use some of the suggested lightweight third party tools to confirm this. They are pretty simple to install and use.
I do not know if GeForce Experience tracks this as well as those tools do, as I've never used it, but if you have it installed you can try to have a look there as well.

That said, a game using most of the GPU while still providing you with good performance is nothing to worry about - I'd be more concerned the opposite was going on.

Thats true. I use Geforce Experience and i dont think i ever seen anything beside the usual update that pops up
on it so i might consider at least look more closely at GPU-Z.

MSI afterburner with Riva should give you decent monitoring during a game. That being said, in modern games, I would expect the GPU to be running between 95-100% at all times assuming you aren't CPU limited (example: Witcher 3 Complete Edition).

It's only in older games where you typically see low GPU and CPU usage in tandem (I wouldn't consider No Man's Sky to be old)

As others have alluded to, it's nothing to worry about if you have good frame rates - GPUs are designed to not leave any performance on the table.

Both programs I've mentioned don't need to be installed to run, just admin elevation :)

Very true, I'm just used to actually having the installed version of HWInfo on my machines

If you can be bothered to read it this article covers how the process can work.
https://developer.nvidia.com/gpugems/gpugems3/part-i-geometry/chapter-1-generating-complex-procedural-terrains-using-gpu
There's some good videos specifically about No Man's Sky as well where they explain how they generate the universe in the game.

But basically noise is the term used for a specific type of random number generation. Normal, purely random numbers aren't much use for procgen, because there can be too much variation from one value to the next which creates unnatural appearance when it comes to textures or terrain.
The kind of noise used in procgen (usually Perlin Noise or Simplex Noise) has two main advantages. First it is contiguous, so values blend smoothly into each other giving a better and more natural appearance. Second it is generated from a seed, and every time a sequence is generated from the same seed it will be the same. So all you need to store is the seed and you can create the same terrain every time.

The calculations used to create noise are much, much quicker on GPU than using the CPU, because the way GPUs are optimised for displaying graphics also makes them better for the numerous but simple number calculations performed in procgen.

I would day that as long as it is not casuing any issues, then the game is just utlizing the GPU to generate what computations it can to the max, especially a completely generated game like No Man's Sky. The onloy time I would worry / care about high GPU usage is when it impacts on performance