Btw I heard that Volume 5 of the manga was recently released in which the author said the manga will be ending in its 6th volume.
Yep, sensei has announced at the end of volume 5 (chapter 25.5, coming soon™) that the story of "Kimi to Tsuzuru Utakata" will conclude in 6 volumes.
She later mentioned on her FANBOX that it was her own decision to conclude the story in the next volume, after discussing it with her editor. There's no external pressure, it's the author's intention.
All volume has 5 chapters each. Vol5 has chapters 21~25. If this remains the same for the next volume, that means it will be ending in chapter 30 and tbh I'm not ready. The manga has 26 chapters btw so in just 4 more chapters the inevitable might be happening.
In the FANBOX post above, she also mentioned that volume 6 "will be a little thicker than usual". So, I'd say around 6-7 chapters instead. (Chapter 26 was already out and it was a bit short because she "was busy", so I counted that as half a chapter.)
She also said that she'll do her best to bring the story to the conclusion, but there might be times when she will have to take a hiatus.
She hopes that we'll continue to support her until the end.