As for Windows 10, the three latest versions – 2004, 20H2, 21H1 – that are fully supported are receiving the same cumulative updates, along with updates rolling out to certain older versions ...
According to the reports, after the Windows 10 20H2 update, apps and programs have lost the colored background that they use to have and now have a color that’s dependent on your theme.
This feature is live in Windows 10 20H2 and later and in Windows 11 too. It does not modify the taskbar for any existing accounts, but only for new accounts or accounts logging in for the first time.