SWIM found that Sprint Layout is the best tool to trace on top of a scan of a pcb and generate Gerbers.

According to SWIM plan :

• install crossover (try staying in demo forever using command “faketime”)
• download Sprint Layout and install using crossover

Sprint Layout

https://www.pcbway.com/blog/help_center/How_to_generate_Gerber_from_Sprint_Layout_6_0.html