As in attached screenshots, when I make Windows 11 taskbar transparent, elements such as: little bar under icons indicating window focus status with the bar changes color and lengthened; mouse hover through icons will make icons having a matte box overylay; multiple windows of same app will having a transparent-matte-ish stack style all display as intended.

Meanwhile DisplayFusion taskbar if choose 'Never render the taskbar backgrounds' in advanced settings, all of above mentioned icon elements will not render, too.

App like Discord that changes its icon when having unread message are kinda okay to get updates from DisplayFusion taskbar. Other than that the taskbar will only shows me what apps are opened, no focus status, no activity overylay, nothing.

Also since I only get DisplayFusion taskbar background back to having a comparison for this issue, I'd say I found that the little bar under icon in DisplayFusion taskbar is not centred. And the stack style icon just looks like icon has a vertical black line on it.