By going from the menu, into the Multiplayer list, adding a new server and starting to type in Server Address would work fine until you select Server Name after Server Address which would cause the caret still be visible but not usable until selected once again.
Evidence: https://youtu.be/XLMS-bTjonY
Thank you for your report!
We're actually already tracking this issue in MC-147605, so I resolved and linked this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
If you haven't already, you might like to make use of the search feature in the future to see if the issue has already been reported.
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