What happens if I change a PNG file to a ZIP file and try to open it in Windows?

What happens if I change a random file into a .zip file and try to open it? Will anything bad happen?

Imagine that I take a .png file, and change the file extension to .zip. Will attempting to open or unzip this folder break anything, or will it just be filled with garbage?

I tried googling it, however all results were about renaming files whilst they are still inside a .zip file, which is not what I want.

I don't know what you consider to be "bad", but all that will happen is that trying to unzip a .png file renamed to .zip will fail. The .png format is entirely unrelated to the zip format. The same would be true of many compressed formats, such as .pdf, or even .gz. (gzip is not zip.)

On the other hand, there are many formats that use the .zip format as a way to package their components. It provides both structure and compression. Office software is a prime example, where .docx, .xlsx, .pptx, .pages, .numbers, .key, .odt, .ods, and .odp are all zip files. All of them can be renamed to .zip and you can use zip tools to peek inside. In fact, you don't even need to rename them to do unzip -l sheet.xlsx. Java .jar files are also zip files, and there are many other examples.

There are NOT enough similarities between some file formats for them to be useful by simply rename the extension, whilst for others it may be beneficial as part of program processing.

You ask about PNG and ZIP where often a PNG can be found inside a ZIP wrapper such as an .oxps or .ora or many office formats.

One simple Windows combination is to right click a set of PNG and "enwrap" as a "Zip folder"

The folder can allow the component parts to be seen individually in the zip.

However if you then rename a zip folder of images as ".cbz" it becomes a Comic Book and the multiple pages can be viewed as an eBook

The easiest way to find out is to actually try it. But no, it will not break your computer. At the most, you'll get some sort of error message saying the file is corrupt. This happens because when you double click on a file, the operating system will attempt to open it using a pre-determined application. For example, a .zip file will normally open with the "compressed folder" feature of Windows. Since a renamed .png does not have the internal structure of a real .zip file, the system will think the file is corrupted. This all happens at the application level, and has no lasting consequences on the computer or its operating system. Hope this answer was informative.