No. In just streak you can only check off today. The month calendar on a habit's detail screen is there to look back, not to edit.
We keep it this way so a streak always means what it says: days you actually showed up.
What you can do instead:
- Check off before midnight. Today counts until the day is over on your phone's clock, so a late check-off still keeps the chain.
- Let shields do their job. If you missed a scheduled day, a streak shield covers it automatically, as long as you have enough for the whole gap. See When do streak shields kick in?
- Undo a mistake. Checked off the wrong habit today? Tap the check again to undo it.
- Use rest days. If some days just don't work for a habit, take them out of its schedule under Edit › Days. Unscheduled days never break your streak.
If you think a check-off you made today went missing, see My check-offs disappeared.