Can't Route Between Networks

I’m trying to route IP 10.165.135.0/24 from Client C through the interface of Client A. Every IP address should route through to the interface of Client B. So, I’ve added a catch all default route (0.0.0.0) for the Interface of Client B. Added a specific route(Distance 1, Scope 30, Target Scope 10) for 10.165.135.0/24 to route through the gateway of the Interface for C.

I’m unable to ping from Client C to any of the IPs (10.165.135.0/24). Could anyone advise what I’m doing wrong? TIA

The image you provided is a bit confusing. is 192.168.88.1 , the only IP of the router? then what are those gateway addresses you set on client A and client B?
it appears that Client A and client B you’re referring to, are not really clients but two different gateways that could be used to access the internet. please provide more info about your setup