I always had a question about the problem of the folder of some site being very heavy, for example, let's assume that I'm using something similar to Bootstrap, in which case I would have several folders of Css/Js/Ajax/Vendor files, etc., but the HTML/PHP page would only import the css folder instead of using the others, having the other folders in the file would influence the loading of the site?
NO, a bulky project folder would not cause your website to load slower.
The way you perceive directories is quite different from the way they actually work. Directories are actually just pointers to where files are stored. The number of directories or files doesn't affect load speed, the server would only render what it needs by querying file paths (an HTML file, image, etc).