Yesterday, having reached her majority, Princess Leonor swore allegiance to the constitution and loyalty to the King before the Cortes
A beautiful ceremony, except the speech by the President of the Cortes, which was pathetic
The Princess wore a white suit and the miniature of the Golden Fleece.

https://www.casareal.es/ES/Actividades/Paginas/actividades_actividades_detalle.aspx?data=15934

After the ceremony at the congress, another ceremony at the Royal Palace, where she was invested with the collar of the Order of Carlos III. The Prime Minister, as chancellor of the Order, passed the collar to the King who, as Grand Master of the Order, invested the Princess.
Later, the Royal Family saluted the guest to a luncheon at the Throne Room.

https://www.casareal.es/ES/Actividades/Paginas/actividades_actividades_detalle.aspx?data=15935

A link to some Brtish media, which have good pictures and some videos

https://www.dailymail.co.uk/femail/article-12692665/Princess-Leonor-sworn-allegiance-Spanish-Constitution-mark-18th-birthday-Madrid.html

https://www.dailymail.co.uk/femail/article-12694481/princess-leonor-crowds-gather-spain.html

https://news.sky.com/video/spains-future-queen-princess-leonor-swears-allegiance-to-constitution-on-her-18th-birthday-12997351