Back in the era of Windows 98, buttons were beveled; one corner was light as if the sun was pointing at it, and the opposite corner was dark, and it made it look like the button was sticking out of the screen. When you clicked on it, the bevels got mirrored as if it was now sticking into the screen.
This showed "I am a button, and you pushed me". But most importantly, it became the universal language for "I am clickable", and you didn't need to hover over it, or click on it, to know that it was clickable.
The same bevel was then used for everything. The scroll bar, the resizable borders, and so on and so forth. If you could click it, it looked clickable
This got dropped progressively in favor of cooler looking UIs, but what we lost in the process is that now, the UI expects the user to have integrated some baseline of "software logic" (I'm trying to think of a software equivalent of "video game logic")
Now to know that something on your screen is clickable, you rely on hovering.
So the result now is that it got even harder to onboard who are new to technology. Most often old people.
They don't even have a legacy "windows 98" theme on Windows 10 & 11 anymore
Even worse is the web, most of the web stopped making links react to hovering, links are not necessarily colored blue or underlined anymore, nothing is unified
How would the web feel if you were the kind of person who didn't instinctively know that clicking on your avatar is supposed to bring you to your user's profile?
The web isn't built for you anymore, the expectations for the user are higher