I just got 10 Gbit internet last week so I had a chance to tidy everything up. The ThinkCentre is the 10 Gbit router, the Synology actually hosts everything.
Also finally labeled all the mystery cables. Also replaced the proprietary 20V/12V bricks for the ThinkCentre and 10G Fiber ONU with USB-C adapter cables to keep things tidier.
It's 6 years old now so I can't really complain but even new ones don't come with 2.5Gbe by standard, it seems that should be cheap enough to throw in there by now. At least a lot of the new ones can be upgraded internally to 10 Gbe.