When WFH started, like most we were actually caught a bit flat-footed in some respects. So I only had my personal laptop to use for WFH too. Before they issued me a laptop, simple acts like logging off VPN, having a dedicated work profile in Firefox and closing _that_, works to compartmentalize my day too.
Finally, best 150 EUR I spent is on a second-hand trekking bike. Nothing like having a hobby that is so different from your work to enforce boundaries. I have other hobbies too but they are physically too similar to work; aside from hobby side projects I also draw and read, etc, stuff that are just as sedentary as programming. The bike let me explore parks and trails I wouldn't otherwise, and even gave me a quicker route to the gym than if I took the bus.