you can modify the keyboard by yourself, following will just add tab key to first page
mkdir -p ~/.local/share/squeekboard/keyboards/terminal/
cd ~/.local/share/squeekboard/keyboards/terminal/
wget https://gist.githubusercontent.com/magdesign/33aa088987d0df044eb75e5a263ca76d/raw/e06dd7535f90037c4c93e91ecf0e6e39afd78611/us.yaml
if you need umlauts use: https://gist.githubusercontent.com/Peetz0r/3cf7d6f8cff6b64f542716fbfd878423/raw/6418ff9fb346aebfe859786b4a9e953e335419dc/terminal.yaml