Possible issues:
1-Your chain and cassette are worn and need to be replaced. Start by checking the chain for wear using a chain checker tool.
2-Your derailleur hanger is bent and needs to be aligned.
3-Your shifter cable needs to be replaced. Try to isolate it by disconnecting it and see if you feel drag.
4-The high limit screw needs to be adjusted on your rear derailleur.
It may be a combination of some of the above.
PS: your chain looks very dry and in need of lube.