Been no official announcements as far as I know , other than a general understanding that United are intending to return at some point and with the right aircraft.
And that gleaned primarily from essence of the press statements back in the winter, and prior the COVID19 recovery strategy .
Specifically Manchester and Glasgow would not return in 2022 - (read NOT never return - a tautology! )
The Max fleet aren’t for crossing the Atlantic whilst the 321LR (XLR) frames that are planned to replace the 757 aren’t expected untill 2024 believe .
And I just don’t see United deploying a premium heavy 763 or 788 as a temporary measure next summer to be honest ( and certainly not if the combined effects of inflation and the deep recession that are expected, go on to knock out significant amounts of discretionary spending - fundamental to serving Manchester in particular)
I might be wrong however for me June 2024 seems the earliest restoration date right now .
I also think Edinburgh may well see some consolidation over the winter period, and that whilst the current plans indicate Washington, Chicago and Newark having an extended operation at the moment, at least one may well be cut back just as has happened this summer .
I seriously expect massive softening in the UK outbound travel markets in the coming months.