How to solve unable to approve solutions cases ?
Requesting you to check whether you have a role assigned with the below option is enabled or not: Admin -> roles
"Allow technician to approve solution".
If not, you will not have the option to approve any solutions (when logged in as a technician), where you can only see a "Submit for Approval" option.
If the option "Allow technician to approve solution" is not checked:
As a technician, you can see:
When the same is checked, 
You can see the below:
