Command + Tab won't restore a minimised app

While holding ⌘ and tapping ⇥ to cycle apps, when you get to an app with a minimised window, instead of just releasing ⌘, before releasing ⌘ hold ⌥alt to restore minimised windows.

the minimised app won't open

This is a bit of a misnomer. The app itself is opened (the macOS term is ‘activated’), as shown by the menu bar changing to display the menus for the newly activated app. It is more accurate to say that the minimised window is not opened (restored).

The distinction is important because I use this feature constantly (it really is a feature!). If I minimise a window, that doesn't mean I no longer want to interact with the app in other ways. For example, a common workflow for me is:

1. Open Finder and work in a Finder window.
2. Minimise the Finder window since I won't be needing it for a while, but want to keep my assortment of tabs etc.
3. Work on something else for a bit.
4. Now I want a Finder window for what I'm working on now. I don't want to restore the Finder window from being minimised, so I'll ⌘⇥ to Finder to activate the application and not restore the window, then ⌘N for a new window.

If you want to switch between apps as a whole, consider taking action on the app rather than a specific window: use the Hide functionality with ⌘H to hide all windows of an app. Then, when ⌘⇥ activates the app, the Show action is performed for you and the windows appear again.

You can always restore minimised windows by holding ⌥ when ⌘⇥.

Use AltTab, it is the exact replica of windows functionality of Alt+ Tab. Takes care of both minimised/maximised window