The dio package 4.0.0 for Dart allows CRLF injection if the attacker controls the HTTP method string, a different vulnerability than CVE-2020-35669.
The vulnerability has been resolved by https://github.com/cfug/dio/commit/927f79e93ba39f3c3a12c190624a55653d577984, and included since v5.0.0.
Cherry-pick the commit to your own fork can resolves the vulberability too.
5.0.0Exploitability
AV:NAC:LPR:NUI:NScope
S:UImpact
C:HI:NA:NCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N