I need some fuel sending unit experts please

A number of things come to mind...

As noted... If the temp gauge works the ivr works.

If you ground the wire at the fuel sender ( very short period of time) and the fuel gauge goes up the wire is good.

BUT....

If the L shaped connector has broken internal wires they might be making connection when you test BUT not when it is connected to the sender.

Also some senders have a nut on the threaded post and that nut can interfere with the connector going on all the way and making contact.

You can connect a jumper wire from the post on the sender to the sender L shaped connector to test if it's a connector issue at the sender.

For the oil pressure gauge...

If you grounded he sender wire at the sender and the gauge did not respond then there is an open somewhere along the path.

Follow it from the engine to the circuit board and see where touching a ground wire causes gauge movement.

If no gauge movement when shorting at the gauge then the gauge is most likely bad. Sometimes you can see a bad gauge by where the needle sits with the power turned off. If it sits well below 0 or the lowest tick that is an indication.