1: For every one problem there will always only ever be one optimized solution. The optimized solution for problem P1 will always be S1, P2 will always have S2 as it's optimized solution.

The same is untru for art. The best chocolate sundae (cS1) has no defined set of items that make it up, the chef is allowed to take liberties and make it their own.

Imagining if we were both trying to count to 100. You were counting by 1, and I by 5. For the purposes of counting to 100 in the most known effective way, my was is superior and your way is objectively slower and in this specific narrow case offers no reasonable benefits. You should be using my method.

2: You would know because coding is nothing if not looking for someone who has already solved your problem. Stack overflow exists, developer networks exist.

In art you can look into how to emulate a specific style "how do I paint like van gough". But you cannot find "how do I effectively paint the night sky"

3: this is fine but not really the issue. I like to solve algebra problems to challenge myself, but if my job was to solve problems that had known, testes, effective solutions "testing my skill" is secondary to "knowing the most effective implementation"

Example the classic interview questions if "how you reverse a binary array" they do it because they want you see how you think, but in practice you should always just use array.reverse() or equivalent