It is extremely important to distinguish the four following categories when answering this sort of question.
Houserules: Tweaks, modifications, or replacements of core systems, e.g., how the game as it already exists works. "Oh, for us, fall damage is d10 per 10 feet, not d6, up to a maximum of 100. Yes, you can take 500 damage from a fall if you fall far enough." These things don't truly "add" or "remove" anything, they're just realigning an existing element in some way.
Personal Homebrew: Genuinely brand-new content created by the GM herself for their game(s). Can run the gamut. Minor homebrew is stuff like "new monsters". Major homebrew is stuff like "new classes with distinct subclasses and signfiicantly new spell lists." Individual spells, items, backgrounds, species, etc.? Somewhere in-between.
External Homebrew: Anything that could've been in the previous category, but which the GM accepts in their game, for whatever reason.
3PP: Actually, formally published rules written by someone else. This includes non-WotC modules.
In my experience, almost all GMs use houserules and personal homebrew, regardless of edition. With 5e, it is extremely unusual to ever see external homebrew. 3PP comes in only three flavors: Absolutely Never, Modules Only, and With Approval Anything Goes. Modules Only is the most common, but it only barely edges out Absolutely Never.
But when you ask about "homebrew" without being specific in these categories, every 5e GM will say they're massively in favor of "homebrew", which gives the false impression that they are extremely welcoming to anything players might find interesting. IME, 5e GMs are very opposed external homebrew of any kind, even when they specifically admit that it looks reasonable.