Finding out what keywords competitors are using is going nowhere

the order that works for me: list 3-5 competitors who actually rank for your stuff (not the ones you think of as competitors, the ones Google shows), drop each domain into whatever keyword tool you have and look at their organic keywords sorted by traffic, not volume. Then do a keyword gap between them and you. The terms two or three of them rank for and you don't are the shortlist. If you've got no paid tool, Search Console won't show you their data, but just googling your main topics and reading what ranks tells you more than people expect.