I just started using Summit, coming from Liftoff that seems abandoned and does not support Lemmy 0.19.
It seems Summit don’t have the ability to show all posts from all multiple accounts in single view, either Subscribed or All. Something for the devs to consider.
This feature can be implemented however due to how the fediverse works any implementation of this would essentially be “read only”. Ie. You will be able to read posts but not comment on them or vote. The reason is because it’s really hard to figure out which account should be used for any “write commands”.