Not really.Whether it contains ramblings or not, a manifesto is a specific type of document with a specific structure. This shooter was clearly a deranged leftist of the extreme woke variety, but they left no manifesto.
From what ive seen on twitter it ticks the boxesmanifesto
noun
man·i·fes·to ˌma-nə-ˈfe-(ˌ)stō
plural manifestos or manifestoes
Synonyms of manifesto
: a written statement declaring publicly the intentions, motives, or views of its issuer