I have solved this issue in several ways.
For UiPath StudioX I found a way around it using Handwriting Detection Activity within Google Vision Package (I have configured the Google Vision connector in Integration Service).
For UiPath Studio that works on a OnPrem Orchestrator, where I do not have an Integration Service and connectors available, I have built a library that connects to Vertex through http request. This library also features system prompt and history capabilities.
Having the http request model made for the automation developers I could replicate the same logic on the StudioX.
I haven’t figured out how to make a custom connector yet though, or how I could import a library made on Studio, in StudioX… This is still something I have to figure out…