The biological species concept remains the standard. If two populations live in the same area, reproduced sexually, and don’t interbreed (in the wild, producing fertile offspring), they are separate species, definitely. This is the ideal.
We’d like to use this standard always. But other organisms don’t care about our need to have neat, mutually exclusive species names to use. They don’t always cooperate.
Hybridization is fairly common between closely related species. Whether it causes us to treat the two taxa as one single species or not depends on its consequences. Are the hybrids fertile? Are they fertile but unacceptable as mates to one or both of the parental taxa? Are they rare? Are they common? Are the parental species becoming less distinct or more distinct with time?
Sometimes hybridization between species introduced in North America is so extensive that they aren’t separate species any more, at least on this continent (Lolium perenne/multiflorum, Raphanus raphinastrum/sativus, some Tamarix species that get ID’d as T. ramosissimum on iNaturalist but are actually hybrids, others). Dr. Mary Barkworth calls this process “despeciation.”