When was first time all F1 cars switch the fuel from leaded gasoline to unleaded gasoline?

[theriusDR3]

in 20th century leaded gasoline were majority usage of our all vehicles around the world. Since the beginning of 21st century, all vehicles abandon the leaded gasoline in favour of unleaded gasoline.

[bhall II]

Googling your question word for word, this what I found...

Formula 1 fuel has been strictly regulated since 1996, when the FIA imposed unleaded fuel that had to meet the Euro 95 standard applied to pump fuel for normal road cars. Prior to this date, Formula 1 had used leaded fuel and chemical additives with very high octane ratings for maximum power.

[Tommy Cookers]

F1 had complete fuel freedom till 1958 (Alfa Romeo/mostlymethanol, M-B/see link, Vanwall/36% methanol 10%nitromethane) so lead was less important
these ingredients having a naturally high Octane Nunber, and outstanding fuel chemistry attributes (ie independent of ON)

1958 compelled pump gasoline (for fuel company advertising), this being unworkable they then allowed 100/130 Avgas
1961 on reverted to 'pump' gasoline (maximum 101 ON)

present Euro road fuel is minimum 95 RON 85 MON (no maximum, so ON is unlimited !!)
max 35% aromatic content (max benzene 1%)
.005 g/litre lead
biofuel component of course
early unleaded (because of a high benzene content etc) was probably unhealthier than the rather lightly leaded fuel that it replaced

current F1 fuel has unlimited ON

http://www.grandprixhistory.org/merc196.htm
http://www.grandprixengines.co.uk/Note_58-2.pdf