Answer by youdont ·
The only issue I had to identify and resolve was a less obvious one that resulted in adding the extra step 7 below (for my own future reference).
1) Back up ReportServer database
2) Back up report server encryption key
3) Uninstall Reporting Services 2014
4) Install SSRS 2017
5) Configure new instance with the same database, credentials, and certificate settings as used by the previous instance.
6) Restore encryption key.
7) Delete old key in ReportServer database that refers the old SSRS instance “MSSQLSERVER” leaving the row referring to the new instance “SSRS”
DELETE FROM keys where InstanceName ='MSSQLSERVER'
8) Test the following: Web Service URL, Web Portal URL, and reports.