For those who are still communicating with words rather than emojis or memes, this Mental Floss article borrows from Lifehacker and provides some tips regarding the use of the subjective ‘who’ or the objective ‘whom’ in sentences.
The article starts out by observing that the words are not interchangeable:
In casual messages with friends or water cooler conversations with colleagues, it might not seem particularly important to use perfect grammar—and saying whom can sometimes make an exchange seem formal in a way that doesn’t match the situation.
In short, mentally swap out the who or whom in your sentence with he or him. If he sounds right, you should use who. If him is the obvious winner, go with whom.
Read the helpful memory prompts here.