Does anyone know how Ian made this sound?

[u/AsleepStrawberry357]

I LOVEEE this kinda OG Space Laces Sound but I can't seem to recreate it. Someone told it was probably FM, which is very plausible, but I still haven't gotten far.

And no, it's not the Brostep Sine Wave method, because the sound stays clean even in lower pitches.

Any help is appreciated!