I need a way to put any chosen window to be always on top.
For example, if I read a book in iBooks or I'm writing code in Xcode using Sublime Text. I want an application or way to overcome the issue.
I tried Helium and Fluid Browser but they are like web browser it's not I look for. I exactly want any application to be on top always for macOS.
Best Answer
Try Deskovery3. It does that and more. (up to and including Catalina)
There's also Afloat (up to Mojave): http://www.perfectlyrandom.org/2016/10/23/always-on-top-in-macos-sierra/
Or AfloatX (for Catalina): https://github.com/jslegendre/AfloatX
Note: these require you to temporarily lower the security settings on your Mac (disabling SIP) during part of the installation/setup.
Alternatively, you might want to investigate the following macOS features: Full Screen, Mission Control, Hot Corners and Spaces which all allow easy and flexible control of application windows.