Go to user settings and disable show read posts, note that this will also hide read posts in the community, saved and profile where the latter two are fixed but they are not included yet in lemmy 0.18.4
It will take a while, it needs to be reviewed, merged and then released. Eta is probably next week for release. And then it depends on where you are getting the app for it to be available.
If you click on that account it swaps to it and then you can sign out at the bottom. But it seems from your previous image that sign out is not visible. Is this container not scrollable? e.g can you scroll down to sign out
Jerboa uses Jetpack Compose toolkit, instead of traditional Views approach. It is not mature yet and the source of many of these problems you are experiencing. It works well with Gboard but not so much with other keyboards.
We cannot solve that issue on our end. It is a problem with the toolkit that we use, see https://issuetracker.google.com/issues/294102838