This unfortunately looks like it could be asbestos dust.
We live in an old building on top of what used to be a workshop, with the garage as a part of our living space, and have just recently discovered these fibres been pouring in to our apparent. So much that I've had really bad respiratory issues.
Over a year or so I've experienced asthmatic symptoms, gradually getting worse. At first I related it to post-covid sensitivity, I never had any kind of problem like this before. A couple of weeks ago, I started to cough extremely much on two occasions and spitted out tons of these from my airways. I also found fibres stuck in the back of my throat and sinuses.
Afterwards I researched it thoroughly, and we moved out last weekend. Despite it being Christmas week.
Basically our (rental) house is falling apart. It's partly built and rebuilt in the 70's. Holes in asbestos insulated ventilation pipes inside the house, asbestos cement wallpaint, asbestos slab attic insulation, asbestos board ceiling and pretty much everything is cracking up, releasing big amounts of fibre. Different types for various materials.
You should definitely make sure if this is the case for you too, it's really dangerous breathing asbestos particles in and known to cause cancer and other respiratory illnesses. It's completely banned from the market since the 80's here in Sweden, and forbidden worldwide to use in any construction at all today.
Hope you are doing well, and that this information can help someone else too.
Some photos documenting our experience with them:





