I'm using i3 with 4k monitors, just set Xft.dpi: 163 in Xresources and that's it. Depending on your applications, you may need to tweak some individually, for example Spotify can be adjusted via cli argument. There's one con, you can't have mixed HiDPI and non-HiDPI displays.
For sway it's much easier, you can have DPI scaling per monitor, but XWayland apps are blurry, so I'm waiting for all my apps to be updated to Wayland. There's experimental sway/wlroots branch with proper XWayland scaling, but I don't have easy way to install it.
For sway it's much easier, you can have DPI scaling per monitor, but XWayland apps are blurry, so I'm waiting for all my apps to be updated to Wayland. There's experimental sway/wlroots branch with proper XWayland scaling, but I don't have easy way to install it.