It might hit a wall, but it is supercharged right now.
It does not look like a sustainable model for the planet for sure. Feels like they build items that are used few days, and then end up in landfill.
Their clothing never lasted as long as clothing from "older" companies, but that's because most of them - especially in the early years of H&M - still were in the business of making things last a lifetime or at least 20+ years. H&M recognized that even if our cloth can be used longer, most of us switch our wardrobe every 5-10 years and made their clothing accordingly.
It's in no way comparable to Shein or kik (don't know if they exist outside of Germany), which make fast fashion in both senses: They quickly replicate the trends, but also make their clothing so cheap that you are lucky if you can wear them a year. And it seems even half a year is impossible with some of their newest things, from that I've read. These companies are in the business of producing garbage, which can be worn on the way between factory and landfill, nothing more.
no doubt that some older pieces are lasting quite well - at this point some are outlasting more recent ones. not limited to h&m, quality seems to be getting pulled down.
brands that were once bought because they would last for 5+ years are still making sales based upon that reputation, but the products aren’t matching.