An HbA1C of 54 is not all that high, the diagnostic level is 48mmo/mol so you are not far into the zone. Some Gp would suggest dietary changes for 3 months before metformin as metformin only helps the body use the insulin it produces more effectively but it has to go alongside dietary changes. You have been given qiute a high dose considering your HbA1C is not all that high.
Many people do find a low carb but not going as far as keto is a successful dietary regime so would have less than 130g carb per day though some people do go lower settling somewhere between 50 and 100g per day. They would determine what they can tolerate by good use of their blood glucose monitor.
It is ALL carbs which convert to glucose regardless of colour so reducing your intake of things like potatoes, rice, pasta, bread, cereals, pastry, starchy veg, tropical fruits as well as cutting out cakes, biscuits and sugary drinks. Basing meals on meat, fish, eggs, cheese, dairy, nuts, veg and salads, fruits like berries with small portions of the higher carb food swill still give you options for filling tasty meals.
As well as your monitor I recommend the book Carbs and Cals or similar apps which give you the TOTAL carb value of foods as well as the info on the back of packets or google searches.