The question of canvas size comes up constantly for beginners and the answer is more consequential than it seems.

Too small a canvas and you're painting in a space that doesn't have enough pixels to support the level of detail you want. The work looks muddy or oversimplified when viewed at intended size.

Too large and performance suffers, files become unwieldy, and you often fill space with unnecessary detail because the canvas demands it.

My standard sizes: 3300x5100 at 300dpi for print-intended portrait work. 4000x3000 at 150dpi for screen-intended landscape work. 2048x2048 for game concept work that may need to be repurposed.

One rule I never break: decide intended use before opening a canvas. Resizing up for print later ruins work that was designed for screen. Build for the output you intend.