Two Poles Three Black Wires and One White - Convert to 120 V Outlets
One of your three black wires is actually connected to the LOAD NEUTRAL terminal so you have two hots and one neutral. Unfortunately, whoever installed this used three black wires and apparently did not mark the neutral.

The wires can be used but you must replace the breaker. Putting a standard 15 or 20 amp outlet on a 50 amp breaker is highly dangerous and against code. You can use either a 240 volt (dual) 15 or 20 amp breaker with all three wires or cap off one of the hots and use a 120 volt (single) 15 or 20 amp breaker.

Two caveats: first, you need to identify the neutral wire and color the ends white, probably with white electrical tape. Second, the wire you have is too large diameter to connect to either the breaker or outlets. You’ll have to make pigtails using 12 AWG wire.

BTW, you currently have a GFCI breaker. You need GFCI protection on outdoor outlets. In my opinion, you’re better continuing to use a GFCI breaker since the outlet will be exposed to the weather and a GFCI outlet will have a short lifespan.