Was doing some arcade mode runs, and game refused to unlock the ending, since apparently the PAL version does not even have an arcade mode ending movie. This means that after winning races on all 21 tracks, even on highest difficulty, the 1 ending movie within bonus items will not unlock in PAL version, as it is the ending movie which is unlocked by playing the gran turismo mode disc. A website confirms this: https://gran-turismo.fandom.com/wiki/Gran_Turismo_2_Arcade_Mode#Bonus_Items https://gran-turismo.fandom.com/wiki/Ending#Gran_Turismo_2
So I suggest that following rule could be changed: "Win all 21 Road Races in Arcade Mode. (Rally courses are not required to unlock the credits) Timer starts at Start Game in Main Menu. Timer ends when the ending movie (in Bonus Items) is selected." It could be changed in a way so the timer ends on the finish line of the last race. Then the player can go into bonus items to show the statistics confirming they have won all 21 road races, as the game will show checkmarks next to the courses
Here is a video of a run I did: I think it makes more sense ending the run at the finish line anyway, it seems like all other categories do that.