Hello @Marcell_Leath, welcome to the community!
It’s a great question. Unfortunately, there isn’t a way to limit what’s shown in the dropdown depending on another cell, though similar requests have come up before (e.g. here).
An alternative approach that might work for your case is to use a “join table” to maintain who participated in which event. I made an example here:
Here, each record in the Participation table links to an event and to a participant, and in addition has a field for whether this participant made it to the final heat. With this structure, you can construct reference lists like you describe using lookup formulas, but data entry (entering who participated and who made it) would be done via the linked “Participation” table instead.