Siegel would return to the championship for the first two rounds of the 2020 season once again driving for Jay Howard Driver Development.[5] He would have a best finish of sixth in his final race.
Siegel returned to the championship in 2020 and switched teams to drive for Jay Howard Driver Development.[7] He took two podiums at Mid-Ohio and finished 13th in the standings.
In January 2021, it was announced Siegel would return for a third season in 2021 driving for DEForce Racing.[8] He would get his first win in the third race held at New Jersey Motorsports Park. He would finish the season 8th in the standings.
DEForce Racing announced Siegel would move up to the series full-time in 2022.[10] At the first round held at St. Petersburg, he would take his maiden win by beating competitor Louis Foster on a late restart.[11] Siegel would dominate the second race held at Barber Motorsports Park starting from pole and leading the race from start to finish.[12] Ultimately, he would end up finishing 4th in the championship due to inconsistency during the middle and latter stages of the season.
Siegel announced in October 2022 he would make the jump up to Indy NXT full-time for 2023, remaining at HMD Motorsports with Dale Coyne Racing.[14] He would finish the season third in points, having won two races and scored a total of five podiums. With this, he also became the season's top rookie.
For the 2024 season, Siegel and HMD reunited for a title assault. At the opening round in St. Petersburg, the Californian scored pole and started out his season with a lights-to-flag victory.[15]
On March 5, 2024, it was announced Siegel would compete part-time in the No. 18 Honda entry for Dale Coyne Racing, sharing his seat with Jack Harvey. Siegel would partake in the four events which do not clash with his Indy NXT commitments, including the Indianapolis 500.[20]
On June 18, 2024, it was announced that Pourchaire had been dropped by the Arrow McLaren team, with the team signing Siegel in his place.[23] Siegel made his debut with the team at the Monterey Grand Prix, where he struggled throughout the weekend, running in 26th at one point after spinning into the gravel; he took advantage of numerous driver errors to finish in twelfth.[24]
(key) (Races in bold indicate pole position) (Races in italics indicate fastest lap) (Races with L indicate a race lap led) (Races with * indicate most race laps led)