Question 1. Previously, the installation logs has always been put in the folder C:\Users\user-name\.TIBCO\, but I can not see any installation log file for RV 8.5.0.  Is it true that the installation log is not stored to disk anymore? If it is, where can I find it?

The Windows native installer of RV 8.5 does not output an installation log file. If you would like to preserve a trace of the installation process, you can click on 'Show details' at the end of a GUI-based installation, right-click in the central panel to show and select the 'Copy Details To Clipboard' dropdown menu, and paste the output to a file of your choice.
 
Question 2. How about Linux installer for installation log file?
 
If installing rpm packages, please refer to the documentation of your rpm installation tool (e.g. yum or zypper). 
 
Question 3. We also noticed that the C:\Users\user-name\.TIBCOEnvInfo\_envInfo.xml was not updated with the new RV information.
 
In the context of RV, the Universal Installer files are mainly used to signal to other TIBCO products that RV is present. If you are upgrading to RV 8.5.x from an earlier version of RV, there is no need to update any Universal Installer file since RV is already marked as present.
 
Question 4:  Can I run the 'old' D:\Tibco\Homes\TIBRV\tools\universal_installer\TIBCOUniversalInstaller-x86-64.exe file to clean up the TIBCO_HOME so that all the files that now are not in use are removed?

Yes.
 
Question 5: With RV 8.5 native installer on Linux, macOS or Windows, Does the concept of TIBCO_HOME does not apply anymore for RV?

Yes, the concept of TIBCO Universal Installer TIBCO_HOME does not apply to RV anymore, although only on Linux, macOS and Windows at this point. This is documented in detail in the RV 8.5 Installation book.

Question 6: With RV 8.5 native installer on Linux, macOS or Windows, Does all the folders inside my present RV HOME folder are now not in use, except for the new D:\Tibco\tibrv\8.5 folder? 
 
Yes, your D:\Tibco\tibrv\8.5 folder holds all of the TIBCO RV 8.5.0 artifacts and these don't depend on anything else.

Question 7. What if the default installation location (/opt/tibco on Linux and macOS and C:\tibco\tibrv\8.5 on Windows) doesn't suit my needs?

-- On Linux, macOS, you could try with "--prefix" option

sudo rpm --prefix /tmp/RV850 -ivh TIB_rv_8.5.0_linux_x86_64.rpm

The --prefix option lets you specify the location of the installation directory. It is called --prefix because it lets you give the prefix that appears in the paths to each of the directories where files from the program or library that you are building are to be installed.

-- On Windows, you can use the following command to install RV in silent mode and specify the installation location:

TIB_rv_8.5.0_win_x86_64.exe /S /D=target_installation_folder

For example:

TIB_rv_8.5.0_win_x86_64.exe  /S /D=C:\tibco\tibrv