On Ash Wednesday and all Fridays during Lent, Catholics are forbidden to eat meat
Is this backed up by Scripture?
By scripture, do you mean the Bible?
Catholics do not depend solely on Sola Scriptura
Regardless of what Christian religion you belong to, the first one was the Catholic Church founded by Jesus Christ and entrusted to the apostles for teaching. As from the first, God speaks to his Church through the Bible and through sacred Tradition. Sacred Tradition
"The Bible is all I need," but this notion is not taught in the Bible itself. In fact, the Bible teaches the contrary idea (2 Pet. 1:20–21, 3:15–16). The "Bible alone" theory was not believed by anyone in the early Church.
It is new, having arisen only in the 1500s during the Protestant Reformation. The theory is a "tradition of men" that nullifies the Word of God, distorts the true role of the Bible, and undermines the authority of the Church Jesus established (Mark 7:1–8).
Although popular with many "Bible Christian" churches, the "Bible alone" theory simply does not work in practice. Historical experience disproves it. Each year we see additional splintering among "Bible-believing" religions.
Today there are tens of thousands of competing denominations, each insisting its interpretation of the Bible is the correct one