Sources: 
Formula 1 currently features 19 circuits certified to FIA Grade 1 status, the highest standard required for hosting Grand Prix events. However, not all Grade 1 circuits are active on the F1 calendar.
Jerez, Sepang, and Hockenheim, despite holding FIA Grade 1 certification, remain idle in terms of Formula 1 action. This is largely due to the intense competition and demand for calendar slots, as well as evolving commercial and logistical considerations.
The pandemic notably reshaped the calendar, with circuits like Portimao stepping in during 2020 to fill gaps caused by Covid-19 disruptions. Portimao's arrival was a direct response to the sport's urgent need for venues amid a ravaged schedule.
Meanwhile, other historic circuits such as Circuit Paul Ricard continue to maintain a presence, having been used as recently as 2022. Paul Ricard boasts an impressive five different layouts approved to FIA Grade 1 standard, underscoring its versatility and readiness for top-tier racing.
Estoril, another circuit with a rich Formula 1 history, hosted the Portuguese Grand Prix for over a decade but is currently not on the calendar.
"With demand to enter the Formula 1 calendar as high as ever, one key requirement for prospective hosts is having your circuit certified to FIA Grade 1 status," highlighting the competitive nature of securing a race weekend.
The status of Jerez, Sepang, and Hockenheim illustrates that certification alone does not guarantee a spot on the calendar, as commercial, logistical, and strategic factors also play crucial roles in determining the Formula 1 race venues.
Sources: Nineteen FIA Grade 1 circuits exist worldwide, but Jerez, Sepang, and Hockenheim, despite their certification, currently do not host Formula 1 races. Factors include calendar demand and pandemic disruptions, with other circuits like Portimao and Paul Ricard stepping in to fill gaps in recent seasons.
