I like HTFY as an album song, but I'm not sure about it working as a single.
Slumber Party didn't flop because it was a bad song or had a bad video, it was mostly Britney not promoting it at all and just doing like three very lowkey performances with Tinashe, who isn't really relevant herself (don't come for me, I actually like her). Honestly, I'm more mad at her for not releasing one of the freshest songs she has released in a long time, which is Change Your Mind. It''s catchy, sounds like the **** Britney we've always loved, and I can't keep imagining how amazing the choreo and possible music video would have been. With the right promo and maybe a latino feature (Ozuna, Maluma, J Balvin, etc.), it had potential to be a top 10 hit, no doubt.