Oleana is fabulous, albeit tough to get into.

I’ve always loved Alden & Harlow, though have not been in five minutes. But it’s a nothing walk from The Charles and a great place for a solo diner sitting at the long bar.

The original Legal’s was in Inman Square, not far away, until it burned to the ground. That was a special place. Unfortunately Legal has gotten less and less special over the last 50 years.

This is a good list. The sad fact, speaking as a Boston resident, is that with the restrictions on alcohol licensing in Boston, all the cool kids set up restaurants in neighboring cities and towns. Pointed out down thread, Somerville is a hotspot- specifically, Union Square. If the OP has specific tastes, we might be able to narrow down some recommendations.