Your browser can't flash over USB. Use Chrome or Edge on a desktop.Flashing needs a secure (https) page.
Install
Connect the Tab5 to this computer with a USB-C data cable.
Pick a version (the latest, unless you are going back to an older one), click
Install devOS and pick the Tab5's serial port (USB JTAG/serial debug unit).
Choose Erase device for a first install. Settings, Wi-Fi and keys are
kept in flash, so skip the erase when reinstalling or changing versions.
When it finishes, the Tab5 restarts into devOS.
If the port doesn't show up, hold the Tab5's BOOT button while you plug it in, then try again.
Updates
Once installed, the Tab5 updates itself over Wi-Fi to the latest version: Settings > System >
Check for updates. The feed is ota/devos-manifest.json on this site.