I've worked for a government entity in Germany where this was regulated as follows. I think most of the private companies do it similarly as a baseline and are more generous as an optional perk:
When you are doing "real" work from home (in bureaucrat-German: "Telearbeit"), your regular workplace is at your home. You need a separate, lockable room, the room needs to be inspected by the employer's safety advisor and data protection officer, equipment such as chair and desk as well the room and electricity are paid by the employer. Safety and health regulations apply in your home same as for the company office, e.g. lighting has to have appropriate brightness, no storing dangerous chemicals like toilet cleaner in the bathroom, etc. Since your office is at home, public holidays (which are location-dependent in Germany), taxes and regulations of your home apply to you. If you travel to the office, it is reimbursed as regular business travel ("Dienstgang"). Any other business travel is reimbursed as having started from your actual starting location (e.g. your girlfriend's) or your home, whichever is cheaper for the employer. But since all this is incredibly onerous and expensive, nobody does "Telearbeit".
The alternative, which everyone uses, is "mobile work" (bureaucrat-German: "mobiles Arbeiten"). That was actually intended as a regulation for e.g. salesmen traveling from customer to customer, only sometimes working from the office. Here, your regular workplace is in the office, meaning that traveling between your home and the office is never reimbursed. Rules, holidays, etc. apply as if you were in the office, even if you are working from somewhere else, e.g. a customer's or your home. Since things are thought to be "mobile" and "random", workplace safety regulations do apply but do not need to be inspected. The employee is responsible for observing them at their current work location (i.e. usually not at all caring about all that crap). If you do "mobile work" from your home, you pay for your own chair, desk and power.
When HR writes emails about WFH and you do pay attention, you will notice that they are carefully avoiding the term "Telearbeit" and maybe even "home office" and phrase everything in terms of "mobile work" (which is optionally 100% from your home) ;)
When you are doing "real" work from home (in bureaucrat-German: "Telearbeit"), your regular workplace is at your home. You need a separate, lockable room, the room needs to be inspected by the employer's safety advisor and data protection officer, equipment such as chair and desk as well the room and electricity are paid by the employer. Safety and health regulations apply in your home same as for the company office, e.g. lighting has to have appropriate brightness, no storing dangerous chemicals like toilet cleaner in the bathroom, etc. Since your office is at home, public holidays (which are location-dependent in Germany), taxes and regulations of your home apply to you. If you travel to the office, it is reimbursed as regular business travel ("Dienstgang"). Any other business travel is reimbursed as having started from your actual starting location (e.g. your girlfriend's) or your home, whichever is cheaper for the employer. But since all this is incredibly onerous and expensive, nobody does "Telearbeit".
The alternative, which everyone uses, is "mobile work" (bureaucrat-German: "mobiles Arbeiten"). That was actually intended as a regulation for e.g. salesmen traveling from customer to customer, only sometimes working from the office. Here, your regular workplace is in the office, meaning that traveling between your home and the office is never reimbursed. Rules, holidays, etc. apply as if you were in the office, even if you are working from somewhere else, e.g. a customer's or your home. Since things are thought to be "mobile" and "random", workplace safety regulations do apply but do not need to be inspected. The employee is responsible for observing them at their current work location (i.e. usually not at all caring about all that crap). If you do "mobile work" from your home, you pay for your own chair, desk and power.
When HR writes emails about WFH and you do pay attention, you will notice that they are carefully avoiding the term "Telearbeit" and maybe even "home office" and phrase everything in terms of "mobile work" (which is optionally 100% from your home) ;)