You won’t be able to exclude particular range of IP addresses (like 192.168.1.10 to 1.25). You can only exclude the range as per below statement.
Based on the size of the subnet, the IP addresses that come before or after the IP address value specified in this field are excluded.
This is by design.
Example:
Subnet: 192.168.1.0 /24
Excluded address: 192.168.1.20
This will exclude addresses from 192.168.1.1 to 1.20. Default Gateway should be 192.168.1.21