Seems to be working again now. ThanksIt‘s still possible, I‘ve just tried it.
Usually, you tap somewhere in the message, wait until you see the magnifying glass/cursor bubble, and then it‘s possible to move the cursor to the desired word/letter.
2nd method:
Tap the spacebar on the onscreen keyboard and hold it for a moment. When the letters disappear, you‘re in trackpad mode, and it‘s possible to direct the cursor wherever you need it.