Finding hooks

I know there are lists of hooks for WordPress like –> https://adambrown.info/p/wp_hooks/hook

But if I want to find hooks for a plugin like WC Vendors there is a much shorter list of hooks like –> https://www.wcvendors.com/kb/list-filtersactionshooks/

Are ‘do_action’ and ‘apply filter’ functions the only thing we can modify?
If given a class like –> https://github.com/wcvendors/wcvendors/blob/master/classes/admin/class-product-meta.php#L10, is there any way to modify it?

Are we limited to the do_action hooks or is there a way to modify other areas as well? Can we use the WordPress hooks to hook into the WC Vendors plugin as well?