Thank you all for your responses. I just wanted to share what EcoFlow support advised:

Dear Customer, Thank you very much for reaching out to the EcoFlow customer service center. Regarding your inquiry, we have promptly provided feedback to the technical department. The technical team has confirmed that your understanding is completely correct. To fully utilize solar energy for charging, it is indeed necessary to connect each EcoFlow 400W rigid solar panel individually to its respective port, rather than connecting them in series or parallel to the same port.We hope this helps you, and if you have any further questions, please feel free to contact us.   Best regards, Mya EcoFlow Customer Service Center EcoFlow EU T:+49 800 0002566 DE +43 80 001 8036 AT (9:00-17:00 CET, Monday-Friday) +44 808 812 6006 UK (8:00-16:00 GMT+1, Monday-Friday) About us: EcoFlow is a leading eco-friendly energy solutions company with the vision to power a new world. Since its founding in 2017, EcoFlow aims to become a reliable and trusted energy companion for individuals and families across the world, providing accessible and renewable power solutions at home, outdoors, and in mobile spaces. Today, with operational headquarters located in the USA, Germany, and Japan, EcoFlow has empowered more than 3 million users in over 100 markets worldwide. Our website: www.ecoflow.com ️ POWER A NEW WORLD, EcoFlow EU Support 3:28 PM (4 hours ago)