You've already done the first step toward fixing your phone, that of cleaning the charging port. Obviously that didn't fix the problem, so now we have to investigate further.
It seems you're not getting a good connection between the charging plug and the connector inside the phone. Since that connector is in constant use, being plugged and unplugged daily, it will eventually wear out, but it could also be a problem with the cord itself.
The next obvious step is to try a different charging cord. A newer cord could give you a better connection even if the charging jack on the phone is worn, but it may not.
If the behavior doesn't change with a different cord, then the port itself may be worn out. You can try looking inside the port with a magnifying glass and a bright light and see if you can find any bent or broken pins; sometimes you can straighten them with a pair of fine tip tweezers. Otherwise, at this point you will probably need to replace the charging port itself.
On your phone it's not too bad of a repair; unfortunately iFixit doesn't have a guide for that, but there is one over at a French site called SOSav.
You've already done the first step toward fixing your phone, that of cleaning the charging port. Obviously that didn't fix the problem, so now we have to investigate further.
It seems you're not getting a good connection between the charging plug and the connector inside the phone. Since that connector is in constant use, being plugged and unplugged daily, it will eventually wear out, but it could also be a problem with the cord itself.
The next obvious step is to try a different charging cord. A newer cord could give you a better connection even if the charging jack on the phone is worn, but it may not.
If the behavior doesn't change with a different cord, then the port itself may be worn out. You can try looking inside the port with a magnifying glass and a bright light and see if you can find any bent or broken pins; sometimes you can straighten them with a pair of fine tip tweezers. Otherwise, at this point you will probably need to replace the charging port itself.
On your phone it's not too bad of a repair; unfortunately iFixit doesn't have a guide for that, but there is one over at a French site called SOSav.
[link|https://www.sosav.com/guides/mobiles/xiaomi/xiaomi-redmi-note-6-pro/connector-load/|Charge connector Xiaomi Redmi Note 6 Pro repair - Free guide - SOSav|new_window=true]