Cloudflare's cPanel plugin has file: /usr/local/cpanel/base/frontend/paper_lantern/cloudflare/config.js and inside is:
"featureManagerIsSSLEnabled": false,

if i set it to true, will it allow cPanel users to activate SSL from within their cPanel accounts? should it be enabled or no?

Cloudflare says that it is likely just a legacy flag that was never removed. In the past, they had a trial run for Universal SSL for partner zones, but SSL is enabled by default for all partner zones now.

so no need to care about the flag "featureManagerIsSSLEnabled".