Synology offers both protocols. You can deliberately turn on/off SMB and/or APFS independently for volume sharing (but only global, not on a per-volume basis), and you can decide wether bonjour shall announce a Time machine volume by SMB share, APFS share or both.

I am running a DS218 as a TM backup and photos volume provider. I am using SMB only without any issues. SMB offers the advantage to be easily accessed by Windows and Linux as well.