Greetings!
I'm experienced in writing web scrapers based on nodeJS, and solutions for automating in-browser actions with iMacros+JavaScript.
Do you really need a "portal" for this task? From how it sounds, something like iMacros would be the best tool for doing this task.
First - you login to WhatsApp web using your phone
Seconds - you run the script, which will look into every one of the user's group, then scroll up to the beginning / last saved point (script will check if there are any), then update the .csv file with new entries: saving separate .csv file for each group
Let’s talk about your project in more detail. Invite me to your job, and I’ll get in touch with you right away to hear more about what you need.
Thank you for taking the time to read my application!
Kind regards, Aleksei