Symphony No. 5 is a large scale choral symphony. It is extant but remains in MS, and it would take lot of dedicated work to produce both orchestral and vocal sets of parts, plus of course there would be the cost of mounting a performance/recording in terms of musicians. So we might have to wait a long time to hear it, if we ever do. A pity, as I too admire Dopper's music and the work sounds intriguing.
Having just written the above, I decided to visit the website of the Cornelis Dopper Foundation, where I found the following piece of news, posted earlier this year and which, because the site is in Dutch only, I put through "Google translate" to produce this text:
The printed orchestral score, the vocal score and the orchestral parts of the first movement of Dopper's Fifth Symphony are ready and the piece can now finally be performed. The “Sinfonia Epica” for large orchestra, choir and soloists on a text from Homer's Iliad Homer was adapted by Marinus Degenkamp and Joop Stam and printed by the Publicom printer in Stadskanaal.
The Veenkolonial Symphony Orchestra, conducted by Lubertus Leutscher, plans to perform the first movement of Dopper's Fifth Symphony. Leutscher has since received the music in print.
The performance of the concert is scheduled for November 14 of this year. However, due to the vicissitudes surrounding the coronavirus, it is unclear whether the concert can already be performed on that date. It is a difficult piece and requires a lot of rehearsal. There is, therefore, a good chance that it will not be implemented until the spring or autumn of 2022.
I am pretty sure we would have heard about it if there had been a performance on November 14th. Nevertheless, the news that performance materials for the first movement of this work have now been prepared is most encouraging.