Not even super massive like amazon, even an app for a few
million users you’ll run into the performance problems of FKs. They are really overrated in their usefulness - as parent says, orphan records are really not a big deal. As soon as you get to any moderate scale, dealing with a small level of data inconsistencies is inevitable.
Especially as you grow into a multiple services, multiple databases type architecture where you fundamentally have to handle breaking fks btw systems
When not using FK constraints, data may be modified or lost (deleted) without proper cleanup of related records leading to "orphaned" records without relationships (or related ids that do not correspond to existing records). The disk space for these orphaned records and the time to run a relational integrity checks across tables (removing orphans), is of minor concern and effort, comparative to a troublesome database entry with FK constraints.