Estimated but probably accurate from recent years. I mostly buy starter packs or at discounts when I really like a game. I think Chromatic Souls is the only one I dropped quickly. Played the rest over months or even years.
20€ on Paladins, Starter Pack to unlock all champions, played this around 100 hours
40€ on Warframe, 50% on Platinum, played this over 300 hours
15€ on One Piece Treasure Cruise, Starter Pack and some Booster Packs for sma money, played this for 1,5 years
5€ on Kingdom Hearts Mobile, starter pack played this for half a year or so
5€ on Mythgard, Starter Pack, actually never used the currency but played it for around 40 hours
2€ on Chromatic Souls, don't know why, played this only a few days lol
5€ on Epic 7, Starter Pack, played for some months
2€ on Final Fantasy XIV for extra retainer
30€ on TESO to buy the first DLCs chapters,so this aren't really MTX but you had to buy the I game currency so it kinda qualifies?