I'm revisiting my Arduino stuff (I want to revive Teleinfo shield to monitor closely my power consumption). I just cannot get the thing to work (Teleinfo Shield + Uno Wifi).

When trying to check what's happening this is the kind of Serial Monitor screens that I get.

Any hints on how to solve? It happens with other Uno as well and different versions of IDE.

Thank for any help, the answers I found in different places didn't lead me to a solution.

I tried several baud settings, (same for port and monitor, each time) and sometimes nothing was written, sometimes complete garbage, sometimes as illustrated

I will attach the code (which is a "standard" that I modified to "trace" what was happening).