His European Tour debut as a professional was made in late November 2019 at the Alfred Dunhill Championship at Leopard Creek CC, Malelane, South Africa, where he finished tied 24th, earning €14,000.

In February 2020, also in his homeland of South Africa, he came close to his first professional win, finishing runner-up in the Limpopo Championship on the Challenge Tour.

In August 2020, Nienaber recorded his first top-10 on the European Tour; finishing 4th in the Hero Open at Forest of Arden CC, England.

[2] In the second round of the Joburg Open in November 2020 at Randpark Golf Club in Johannesburg, South Africa, Nienaber hit his drive on the 597-yard, par-5 4th hole a European Tour season record 439 yards.

[5] He eventually finished in second place; two shots behind Joachim B. Hansen, and reached a career best 209th on the Official World Golf Ranking.