Had this issue where I had tried to install standard edition of SFB server in my lab along with monitoring and archiving databases on the same server. (Got to know later that monitoring and archiving will need a full edition of SQL and not just express edition used in standard edition of SFB)
So, this somehow seemed to corrupt the SQL database, I saw only RTC instance created, and error used to come that there's no Default instance of sql and that login failed with 3 attempts and that there's no xds database. Basically I wasn't able to publish the topology successfully besides multiple attempts.
Since I wasn't that good in SQL, I went for reinstalling SFB 2019 as this was the first server in lab.
So I uninstalled admin tools and sfb server 2019 from "programs and features", uninstalled ucma, uninstalled SQL server as well.
Now, while attempting to reinstall SFB using setup.exe, it gives me a pop-up stating "Access to path server.msp is denied." Many blogs denoted issue to be known in edge server however didn't find anything related to Front end server as such.
Went for installing procmon, and then ran setup to see what exactly is getting denied.
Saw the below for server.msp:
We see that its denoting to the cached files in "C:\programdata\Microsoft\Skype for business server" from the previous installation and unable to delete this specific server.msp to go ahead with new install.
Since this was a fresh install, I went ahead and deleted the entire "Skype for business server" folder in programdata. Now the installation setup.exe went ahead.
Note: if this is production server, the admin can explore giving permission to the specific file which is not getting deleted (with result "CANNOT DELETE" as shown above or look for "Access denied" result specific to setup2.exe process.