Two different things here. As a backup target, Tencent COS is S3-compatible, so you can add it in VBR as S3-compatible object storage. As far as I can see it’s not in the Veeam Ready database, but Veeam states it supports any object storage that implements the required subset of the S3 API with v4 signatures, Veeam Ready or not. That said, there’s an R&D forum thread where someone couldn’t add COS as a repository, so I’d test it properly before relying on it.
For restore, VBR’s “Restore to public cloud” only covers Amazon EC2, Microsoft Azure and Google Compute Engine, so there’s no direct restore to Tencent CVM. You’d need an agent-based approach, restoring into VMs you’ve already deployed there.