It can be hard to give feedback. You have to absorb a lot of context to do it well. You have to make sure the recipient is ready for your feedback. Most importantly, you need to be sure you're the right person for the job.
You should always consider the context around what you're providing feedback on. For instance, a UI Design generally exists to enable a user to carry out a task. But there's a lot of context: Is this a redesign? Were there other designs considered? Is this one screen in a series? How does it fit in with the rest of the UI? Answers to these questions affect your feedback on the design.
There's another, meta-level of context: the designer's own intentions. Are they pushing their own boundaries? What assumptions have they made? Are they proposing an unpopular idea? Who are they presenting their work to? The creator's context for a piece of work is often as important in determining how to provide your feedback. Which brings me to...
Is the feedback-seeker ready to receive feedback? Sometimes this is obvious: they have a rough idea they're bouncing off of you. They've given it little thought – your feedback is essentially part of their brainstorm. It might be helpful, but it isn't likely the idea is ready for critique just yet.
Other times, work is freshly completed and the creator is proud of their work. They worked hard and they feel ready to present it. Often this is a red flag. When a work is freshly finished, the ink is still wet and, especially if it's good work, their heart is still in it. This can lead to defensiveness - a key indicator someone isn't ready for feedback. You want to avoid giving feedback at this time because it can't be received well. You don't tell a mother she has an ugly baby, especially the day its born.
A good rule of thumb: give the creator about half the time it took them to finish the work before sharing your feedback with them. I've found this is a good cooldown period. In any case, no more than a couple days should be necessary.
I don't study game design very closely. I love games. I play them from time to time. I'd call myself a casual gamer. But if I had a friend who wanted me to weigh in on the design of their game or their rendering engine, I'd have a limited ability to help. I don't have the expertise.
Sometimes, when someone comes to you for feedback, you just aren't the right audience for it. It's okay to admit this. Just make it clear that you can only speak with a limited perspective. They'll understand, especially if they want to make something well.