One of the balloon techniques listed on Blambot’s comic grammar page is “breaking borders”. For this type of balloon, Nate Piekos writes,
[Balloons breaking borders] seems to be more prevalent in hand lettering. I suspect this is because doing it digitally generally adds an extra few steps that can take time to do properly and cleanly.
In Inkscape, a lot of things are being done manually already when it comes to making a comic, so a few extra steps here and there isn’t that big of an issue. For balloons breaking borders, it’s actually not too bad. Essentially, “Difference” is your friend. Anyone not familiar with the “Path” menu items for adding and subtracting between objects should play around with them, and get to know them. It’ll help develop ways of doing things, such as with a balloon breaking the panel’s border.