OSX- Missing Merge Windows Option.

Hello everyone.

am struggling to restore my previous look when opening multiple instances of IntelliJ.
Before if I had a couple of running Intellij instances when clicking on the icon reside on the dock, I had the ability to switch quickly between windows using the popup upper tab bar which was open when closing my mouse cursor to the top of the window.
somehow after upgrade to the latest version of IntelliJ now this popup tab bar missing. and the same instances are no longer grouped under the same window.
when I checked in some threads on the net, I found out that I need to activate this specific preference through Settings-> General-> Prefer tabs: Always OR in full screen. I set it but still, same behaviour - no grouped instances and no tab bar open when moving my cursor to the top of the window.

my details :

IntelliJ IDEA 2020.1.2 (Ultimate Edition)
Build #IU-201.7846.76, built on June 1, 2020
Licensed to Kobi
You have a perpetual fallback license for this version
Subscription is active until July 19, 2021
Runtime version: 11.0.7+10-b765.53 x86_64
VM: OpenJDK 64-Bit Server VM by JetBrains s.r.o.
macOS 10.16
GC: G1 Young Generation, G1 Old Generation
Memory: 4096M
Cores: 8
Registry: debugger.watches.in.variables=false, debugger.valueTooltipAutoShowOnSelection=true, compiler.automake.allow.when.app.running=true
Non-Bundled Plugins: com.github.chencn.yamlandprops, Lombook Plugin, aws.toolkit, me.mbolotov.cypress.pro