Yes I faced the same problem and got panick. googled and found your solution. I tried with many different cables and plugs which all work with my other samsung devices. This A51 only recognizes the plug and cable that was in the box. Others after few seconds goes on/off just looping.
Hi, I found out that those el-cheapo $2 "Samsung Type C" cables selling online do work. As long as it stated "Samsung Type C" on the title.
But premium brand 5A high quality cables will not work.
So, no fancy braided stuff for the A51.
Anyway, just bring your A51 to an Accesories phone shop to try.. Many.. One is sure to work.
Too bad in stores or online, can't find a 2M cable.