Even AptX doesn't have the complete bandwidth for lossless like FLAC, but if you're streaming a 320kbps file, it will technically be lossless in that there are no losses as its bandwidth can handle that with no problems.
Either way there are other bits involved in the audio chain that have a bigger impact than just BT bandwidth and losses. If you're using a BT headphone, there's the question of how close to flat the drivers are, and that assumes the amplifier in the BT circuit isn't struggling driving it. If you're using a BT dongle, then there's the problem of how good its DAC and amplifier are, especially when you hook up a relatively hard to drive headphone, or in some cases, the impedance might actually be too low.
Personally though I only use BT when I'm streaming to some convenient system in a non-critical listening situation (ie I won't need to sit properly relative to the two separate speakers), like grilling out in the yard and we just take turns using our own phones to control the music coming out of Bose water-resistant (ie we clumsily hope it's beer- and cow "blood"-resistant) speakers, and in this situation there are no downsides to BT. We're not listening critically, the speaker doesn't need a lot of power if it can sit in the middle of the table (and can survive toppled beer bottles and rare beef dripping on it), each phone has a Spotify account or local storage and it works like how we used remotes before (except back then I'd have to walk up to the window and hit "Next Disc," only to realize that the dad's 300-disc changer's catalogue has errors). Anything more private and/or critical than searing a porterhouse rare while Slayer's "Reign in Blood" plays in the background as a joke, I skip wireless, primarily because I don't mind wires when I'm not dealing with tongs, fire, and meat, and certainly not to the point of having to sacrifice quality of the other components (again, BT itself isn't the problem) vs my preferred high sensitvity IEMs for example. Even when jogging I'd rather deal with getting a new cable on an ergonomic-fitting IEM than dealing with batteries on BT headsets.