en.wikipedia.org/wiki/Cesare_Borgia

The claim conflicts with local and reference histories of Cesenatico.

• The official tourism site for Cesenatico states that the canal port "was built in 1314" and that in 1502 Cesare Borgia called Leonardo da Vinci to help with the problem of sand bars silting up the harbour entrance.
• Treccani’s encyclopedia entry on Cesenatico likewise says that in 1501 an engineer of Cesare Borgia wanted to extend the navigable canal toward Cesena, and that on 6 September 1502 Leonardo was at Cesenatico and made a survey of the port.

So Leonardo did not build the canal port itself, and the evidence here points to a survey/engineering inspection rather than the construction of a canal from Cesena to Porto Cesenatico.

Accessible museum and regional-history sources show that Leonardo did obtain major patronage in Italy after serving Cesare Borgia.

• The Museo Leonardiano di Vinci biography states that in 1503 Leonardo returned to Florence, where he was commissioned by the Republic of Florence to paint the Battle of Anghiari.
• The same biography says that from 1508 to 1513 he was back in Milan in the service of Governor Charles d'Amboise, and that in 1513 he moved to Rome under the patronage of Giuliano de' Medici.
• The Museo Galileo / Leonardo’s Tuscany page on the Battle of Anghiari likewise says that in 1503 Leonardo received the prestigious commission from the Republic of Florence to decorate a wall in Palazzo Vecchio.

Those documented commissions and patrons directly contradict the statement that he was unsuccessful in finding another patron in Italy after Cesare.

Alexander VI was notorious for openly acknowledging his children, but he was not the first pope to do so.

• The Catholic Encyclopedia entry for Pope Innocent VIII says that before entering orders he had "two illegitimate children", Franceschetto and Teodorina.
• The 1911 Encyclopædia Britannica entry on Innocent VIII adds that as pope he "openly practised nepotism in favour of his children" and specifically advanced his son Franceschetto.

Because Innocent VIII reigned before Alexander VI (Innocent VIII died in 1492; Alexander VI succeeded him), the statement that Alexander VI was the first pope to openly recognize such children is false.

The modern jurisdiction "Archdiocese of Pamplona and Tudela" did not exist in Cesare Borgia’s lifetime.

• Catholic-Hierarchy’s entry for Cesare Borgia lists him as "Appointed Bishop of Pamplona" on 12 Sep 1491.
• The official history page of the Archdiocese of Pamplona and Tudela says Tudela was erected as a diocese only in 1783, that Pamplona was elevated to an archdiocese in 1956, and that the permanent union of Pamplona and Tudela under one prelate dates to 11 August 1984.

So describing Cesare in 1491 as bishop of the Archdiocese of Pamplona and Tudela projects a much later church structure back onto the 15th century. The historically correct formulation is that he became bishop of Pamplona.