Can I work with multiple NGOs while having a permanent job?

I know it looks a little confusing. I am someone who works in a big MNC and also work in our societal NGO. Not gonna lie I feel more connected to the work I do at the NGO than my actual boring 9-5 job. So since it's a societal NGO they give me some salary ( since we are like a family and everyone insist) so I donate 50% and take home 50%. Since I am loosing more and more interest in my jobs. I was wondering if it's possible to work for multiple NGO at the same time. Do big MNCs allow this (consider Deloitte, accenture, BCG and FAANG). Also if they allow where can I find such opportunities? My qualifications- senior marketing manager