The United Methodist Church's "Ministry Matters" online magazine has published an article with numerous links to other articles dealing with "the attendance question" --how churches are preparing and changing.
Here's a quote from the article:
The answer to the anxious question for leaders--Will the people return to the sanctuary?--is necessarily delayed until the delta surge burns out. However, before the surge, anecdotal observations registered alarm concerning low worship attendance in June and July (which applies to in-person or a hybrid online environment). It’s summer, with vacations as a factor, but the challenge for the return is still obvious.