The reason I'm bullish on Summer 2022 is because by the end of this year, everyone (of all ages) who wants the vaccine would have gotten it and with the weather change, DJF will be the the critical test to see if we experience another surge like we did this past winter.
But even then, there may still be some form of travel restrictions to/from a small handful of countries where the health care infrastructure and vaccine distribution remains poor.
EDIT: Also, any lawsuits related to COVID spread in shared public spaces will hopefully have been litigated by then, establishing a precedent that businesses can confidently adapt to accordingly.
This is just my gut feeling though.