Found mismatched breaker and wiring while replacing kitchen outlet in older house
I'd add a new 12AWG homerun from the panel to the junction box

What I'd do here is put a new 12/2 homerun in from the existing 20A breaker on the circuit to the junction box where the 14 and 12AWG wires are split, then connect the wires in the junction box by size as well as color (12AWG black to 12AWG black, 12AWG white to 12AWG white, 14AWG black to 14AWG black, and 14AWG white to 14AWG white), save for the grounds which all connect together.

At that point, you can take the existing 14/2 homerun off the existing 20A breaker in the panel and land it on a new 15A breaker fitted in one of the open slots on the bottom left -- Eaton CH breakers are widely carried by big-box stores and supply houses across North America.  (If you need to splice some extra 14AWG onto the end of the homerun to make it reach, go ahead and do so with a wirenut -- splicing in a panel is safe and Code-compliant, even though some ignorami misinterpret the Code that covers this to say otherwise.)

You can then fit a 20A GFCI to the 12AWG (20A) circuit to protect the dishwasher and receptacle.