I am also not an accountant, but in my country even a failed business project is still a business project. E.g you run an IT consultancy and suddenly decide you need to do something with AI. Wellll now that gaming PC with a really over the top GPU is actually a business purchase because you NEED that VRAM. AI project didn’t do all that well? Oh well, shit happens. Keep the PC tho, maybe you’ll need it for another project soon.

Home office is another fun one. In my country, you have to decide what % of different purchases are for business vs living use, for tax-free expense compensations. But the interesting thing is, you can go really in depth with that. 20-40% of your toilet paper could be business usage reasonably, depending on what percent of awake time is spent working vs not working.