This is correct and I'm not sure why it's been downvoted. In Germany, you'd better only every use the work-room for work only. As people have pointed out, you're not likely to get audited for this but often, with apartments, it can be quite obvious that you're using the space for non-work stuff too (for eg, if you're living in a 50 sqm apartment, it's pretty easy to say that you can't possibly have a dedicated work only room).
In the US, my accountant always (and as I understand it, the rules have gotten stricter) recommended against taking a home office deduction unless you really had dedicated space for equipment etc. and didn't have an office you could reasonably commute to. The way more typical "office space you often use for doing work" was long seen as a red flag for a deduction and, in the typical case, as you say, truly dedicated space is rare absent a large place and/or specialized needs.
I could make a room a dedicated day-job office but it would cost me way more to do so than I would ever get as a deduction and it would almost certainly be inferior to the mixed-use setup I use.
This is such a perverse rule. You don't have enough living space? You can't possibly claim compensation for being forced to also use that as a workspace.
Sure, many don't. And many people have found that the tax office does inspections from time to time. That's not a pandemic issue, the laws and the jurisprudence have been in place for decades.
But you just have to love how HN endorses tax fraud.
You've got a computer in there that you're also using for private stuff? Not tax-deductible anymore.
Private books on the bookshelf? Not tax-deductible anymore.
You've got a wardrobe with some clothes you're only accessing once per season (to store off-season clothes)? Not tax-deductible anymore.