This can't be stressed enough.
With phones and the Internet today, most of us consume way more information than we have time to really process, organize, and reflect on. It's like we do a shopping spree every single day and never spend any time in our house unpacking any of the grocery bags. Our minds are a chaotic mess of piled up worries, news, unmade decisions, etc.
Walking (without audiobooks or other media) is the single best solution I've found to give my brain the idle time it needs to run a defrag and work through that backlog.