It's true for HDDs. They don't maintain a list of compatible third-party HDDs, but you use them perfectly fine. No errors, drive health monitoring works, etc.

https://www.guru3d.com/story/synology-reverses-policy-bannin...

>Now, with the release of DSM 7.3, Synology has quietly walked the policy back. Third-party hard drives and 2.5-inch SATA SSDs can once again be used without triggering warning messages or reduced functionality. Drives from Seagate, WD, and others will work exactly as they did before—complete with full monitoring, alerts, and storage features.

NVMe SSDs are different.