I've been creating and managing a e-commerce website with my own brand for about 3 years and Facebook ads have always been my main source of income (selling mostly t-shirts) so I'll give you feedback about my own experience in the fashion industry.
To begin with, I don't know why exactly but I feel like Facebook ads have diminished in terms of efficiency and ROI, especially retargeting ads (while mine reached a ROI of 7/8 about 2 years ago, now it dropped to under 3). However, they still can be profitable but I think they depend a lot of the products you are selling.
For T-shirts and fashion in general, I'd say you'd need strong and original designs to draw attention, clicks and comments. Orienting your brand or your marketing with some strong, dividing topics will help with comments and people reacting and feeling attached to your products (topics like veganism for instance). I also think those ads start getting effective after your created a bit of a social following so people trust your page more, at least 1000 real followers you earned the hard way. You will then probably first need to use some budget that won't generate sales. Facebook gives a grade out of 10 to your ads, so only boost the ones which get at least 8/10 or you will waste money (the higher your grade, cheaper you get social signals).
So I'd say if you're just starting: start with posts that will draw attention and followers and promote them until you have a bit of credibility. Then switch to conversion ads (mix quite a lot of different ones in one campaign, and create different groups inside them to test different audiences until your Facebook pixel registered enough sales to be precise on who he is gonna be targeting thanks to your customer list). Try different formats, different type of copywriting until you find the ones which speak to your audience.
When it is done, you shouldn't have too many problems havings ads with at least 3X ROI, which will make you money as long as your margin is not too low. Even better if you have a pretty high budget to spend (because you will have to pay Facebook each time you reach 500$ spent in ads).
For instance of a really recent success story, I have a friend who didn't know much about e-commerce at all. She created a dropshipping website with Shopify with a friend of her 9 month ago, and they are now making about 25000$ net profit a month on girl's fashion products spending about 200$ in ads a day. If you check their website, their DA is like 4 as they don't know anything about SEO, but they don't need it as their facebook ads are really effective thanks to the way they chose their products and designed the brand of their store!
In conclusion, it still works but it depends on what you sell, your brand and your audience.
What have you tried with FB that it fails completely ? What are you selling in other words - let us all know, it may depends on the product as well.
