The only big deaths we've had in the MCU are:
- Stark: obvious
- Widow: pretty depressing really, really heavy, really memorable
- Yondu: really well done scene gave huge weight to the character
- Vision: low key dark AF, really heavy, really memorable
[- maybe Loki: dark AF, and the voices of 10 billion fangirls/boys cried in unison]
Hell, if you want, you can add Frigga to the list, since they had a whole ass funeral for her, in one of the best scenes in the MCU period.
That is a standard in the MCU for big deaths. (and no, QS, TAO, and whoever is introduced and killed in the same movie doesn't count, they were barely around)
Good freaking luck.