Kindly refer to the following links:
Praying Sunnah of Fajr after Fard | Sheikh Assim Al Hakeem
Can I pray the Sunnah after the Fard Prayer without any valid reason?
Came late for dhuhr congregation, can I pray all sunnah prayers together after fard?
Came late to the masjid, can I make up sunnah prayers of dhuhr after the fard prayer (legitimate excuse)
Can I make up sunnah prayers of fard salah even if their time has ended?