I use Notepad2 as a direct replacement for Notepad - it's a single binary that's a few hundred Kb in size, supports syntax highlighting (with customisation) for

I use Notepad2 as a direct replacement for Notepad - it's a single binary that's a few hundred Kb in size, supports syntax highlighting (with customisation) for most major languages, regex search and replace, rectangular select, coding-friendly text tools (change case, toggle comments, indenting etc), code folding, and handles different encodings and line endings. If I need anything more then I'll use VS Code, but for single file viewing and editing it's perfect for me.