4K is most definitely NOT the standard yet. Not even close. 1080P has been the standard for many years and still dominates the market. In fact, on the recent
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, 1080P accounted for over 54% of user's monitors still, while full 4K (3840 x 2160) was only about 4.5% of the market.
4K is nice on large displays, like TV's, but it's mostly wasted on PC monitors under 32" and mobile devices.
Personally, I save 4K for my special renders I give out as a perk to my subscribers. For production renders, I work in 1440p mostly, then downscale to 1080P webp's. I find that is a good balance between quality and speed of rendering. I did a whole update once in 4K and the extra time to render wasn't worth the final result, since my VN's are in 1080P and will remain that way for the near future. Heck, I am starting a course in professional animation soon and the college uses $2000 Wacom tablets that are 1080p as well.
I think, for most mobile devices and web based art, 1080P is perfectly fine. You can do 1440p and downscale as well. I learned early in my art training (long long time ago) that you should work big and save small. Never the other way. But if you are planning on making prints of your art, then - yes - working in 4K would be best for that.
There's also a big difference between hobbyist work and professional work. If you're just doing this as a hobby, it's fine working in 4K, but if you are trying to sell your work, production time becomes a big issue. That's why it's important to learn your editing software as well. Doing post production work in Photoshop, for example, can save a ton of time, over trying to do everything in DAZ or whatever rendering platform you are using. For example, I recently did an animation series for a dance, and the difference in rendering time between doing it in 1440P and doing it in 1080P was almost 6 hours more, for 1440.
In any case, that's my experience with it. You need to experiment and create your own workflow.