If we deploy UE script to JE and create amortized JE, does that UE script runs?

No because it’s a system generated JE UE can’t run another UE

Instead of UE, what about making it as a Workflow Action Script. Create a workflow and call the WAS with "After Record Submit" trigger. I haven't try, but maybe it could work, because unlike UE, Workflow is executed even when the record is created from the script

It all depends on the action in my opinion. But WAS it’s like an UE so for me it’s not working But imagine if WAS working , If the need is to modify a lot of data on a amortization/rev rec journal, the time/governance limit will be reached very quickly. To have often worked on JE generated by the system, nothing more better than an MR

Thank you all