So I think that there might be several problems here. JSONToFeatures does not seem to want to output to the "memory" space but it will write to "in_memory"; however, after writing, it does not show up as a feature class using ListFeatureClasses-- --even though it appears as such using describe.
import arcpy
#rename to your path, and replace .txt with .json
json_input = r"WHATEVERPATH\test.json"
arcpy.env.overwriteOutput = True
try:
arcpy.env.workspace = "memory"
arcpy.JSONToFeatures_conversion(json_input, "json_output")
except Exception as e:
print(f"There's this 000206 Error when running the {arcpy.env.workspace} workspace:\n\n{e}")
arcpy.env.workspace = "in_memory"
arcpy.JSONToFeatures_conversion(json_input, "json_output")
print(f"But it seems to work fine running the {arcpy.env.workspace} workspace")
print(f"\n\tThis item exists: {arcpy.Exists('json_output')}")
json_in_memory = arcpy.Describe("json_output")
print(f"\tThis item is a: {json_in_memory.dataType}")
print(f"\tThis item is located at: {json_in_memory.catalogPath}")
list_fc = arcpy.ListFeatureClasses()
print(f"\n\tBut, when we check our current workspace {arcpy.env.workspace}, it returns no feature classes {list_fc}")
Using the Python Kernel from ArcGIS Pro 2.7.1
Likes an array of [cats, gardening, photography]