I want to use a longer cable (50 cm or more) from the mini 2 USB C controller port to the micro USB port of my mobile (Redmi Note 5)   
Which type of cable is suitable? There are obviously some major things to consider, e.g. "OTG" or the direction of data transfer and the loading direction.(e.g. data transfer only in one direction, which doesn't work for a connection from controller to mobile, which should be a two way connection)
Your advice is highly appreciated.

wolfg47, try Anker.com, I have gotten multiple types of cables from them, and all work nicely.  I have a couple different length cables for between the Remote Control and
a Mini-4 TAB.  No problems.

Hello there wolfg47. Good day and thank you for reaching out. You may try check our DJI Where To Buy platform on this link ( https://www.dji.com/where-to-buy ) to see if those cables that you need is available. In addition I hope that you can get some recommendations from our DJI Co pilots with regards to this inquiry. Thank you and please be safe always.

That is a very long cable. How are you using it?

Did you ever find a cable? I have a Lenovo TAB4 M8 with a micro usb port and need to find a cable that works.