Вроде бы сделал связь, ура победа

app/src/main/java/com/example/labwork/models/Bicycle.kt

@@ -1,9 +1,14 @@
 package com.example.labwork.models
 
 import androidx.room.Entity
+import androidx.room.ForeignKey
 import androidx.room.PrimaryKey
 
-@Entity(tableName = "bicycles")
+@Entity(tableName = "bicycles",
+    foreignKeys = [ForeignKey(entity = User::class,
+        parentColumns = ["id"],
+        childColumns = ["userId"],
+        onDelete = ForeignKey.SET_NULL)])
 data class Bicycle(
     @PrimaryKey(autoGenerate = true)
     val id: Int?,

app/src/main/java/com/example/labwork/models/UserWithBicycles.kt

@@ -1,13 +0,0 @@
-package com.example.labwork.models
-
-import androidx.room.Embedded
-import androidx.room.Relation
-
-data class UserWithBicycles(
-    @Embedded val user: User,
-    @Relation(
-        parentColumn = "id",
-        entityColumn = "userId"
-    )
-    val bicycles: List<Bicycle>
-)