The Realtek HD Audio manager isn't available on a recent (end 2020) Windows 10 system. The Realtek Audio chipset is on a Gigabyte mainboard.
- Install the Realtek HD Audio driver from Gigabyte, not from official Realtek site. Note: There is no universal Realtek driver (yet), there is an unofficial one on GitHub though, but its installation requires multiple steps, system files/settings modifications, etc. Installation may require one or two subsequent reboots, first the setup uninstalls the existing/old/incorrect Realtek Audrio drivers, then reboots and the setup automatically starts itself (be patient!) after rebooting and logging in to install the new driver.