Some kind of bug. Haven't heard of this. Try to reselect the theme from the standard ones, switch the day / night mode settings. Judging by the taskbar, mixed night and day modes.
Tried, but the glitch is still there. I also tried to disable and re-enable transparency effect, but nothing change.
@alessio89g I think that there is no particular problem, but the problem is in the choice of settings. I think it's because I can't check at the moment because I don't have any Windows 11 here The probable reason could be this: You have enabled the automatic accent color under the "Choose your accent color" selection on the settings panel and you have also enabled the accent color for the title bar and window borders. Check, this is my opinion.
I found the solution. I noticed that when the navbar wasn't black, it had the Mica effect, but in my laptop (where I don't performed an upgrade, but a 22H2 clean installation, and the glitch there wasn't) the navbar is always white. I remembered that in Explorer Patcher there was an option to apply the Mica effect in the Navbar too, but in recent builds it there is not. So I downgraded to an old build (May 2022), where the option there is, I updated again to the newest build an the glitch is gone.