When I use mouse, clicks on the tab bar not only switch tabs, but also activate links/buttons/other active elements of the displayed page underneath where I clicked (if there are any). The Menu and the Plus buttons also trigger elements underneath them.

I have recorded a video to show the behavior.

The behavior is the same whether I use Logitech MX Anywhere 2 over bluetooth, or BTC 9039ARF (keyboard with built-in trackball) over USB, or both at the same time.
But when I tap a tab using finger, it just switches the tab, nothing on the page is activated.

Opera version is 61.2.3076.5649. Android 10. Shell is Samsung One UI 2.5.