I have the exact same problem. I am running Unity 2019.4.20f1 and I was looking to integrate the compatible Wwise 2019.2.9.7459 into the project two weeks after my team had made some headway on the project. It hung on the "Executing Unity to complete the installation. This may take a few minutes, please wait..." dialogue. As Adam suggested, I tried the workaround, and while it took a few hours, I had some success. I will detail my process here in case any specifics help those who run into a similar problem.
I created a new, blank project of the same unity version and integrated wwise into that project. I then took the wwise folder that was introduced into the project folder and copied/moved it into my destination project. Then I took to editing the code as Adam suggested:
AkWwiseProjectInfo.cs is found in:
C:\...\projectName\Assets\Wwise\Editor\WwiseWindows
c.s.49:
#if UNITY_2019_3_OR_LATER
change to -->
#if UNITY_2019_3_OR_NEWER
I also had to do make the following change, but I'm too inexperienced with C# to know if it really changed anything.
c.s.54:
else --> delete
insert 'else' below '#else' on c.s.55
Move Wwise folder from blank project asset folder to destination project's Asset folder
Manually create a StreamingAssets folder within ProjectFolder that contains folders as follows:
C:\...\ProjectFolder\Assets\StreamingAssets\Audio\GeneratedSoundBanks
Using the Wwise editor within Unity's project settings, ensure that the SoundBanks Path under Asset Management is set to the GeneratedSoundbanks folder that you just created within StreamingAssets.
Soundbank generation should properly configured according to the end of the first part of the Wwise tutorial by AudioKinetic, including overriding soundbank controls and setting up the correct Windows folder within the Soundbanks folder in the Wwise project, not the Unity project assets folder. Soundbanks\Windows is very different from the created GeneratedSoundbanks direcory.
I created a new Wwise project and then saved it within the Unity project folder.
After these changes, and constant fiddling with the directories to get the above, the sound engine was initialized successfully in my Unity project and the Wwise Launcher could find the wwise project file within the context of the unity project.