I develop a roguelike deckbuilder (Way to Crown) with rich and complex set of mechanics, so lots of playtesting is needed.
Due to complicated nature of gameplay, players keep finding non-trivial bugs even to this day, you can see some examples of past bugs in the dev log.
Another task I have is game balancing, which, although somewhat different from pure QA, can also be considered important experience.
This is a hobby project, so we do not have deadlines or other kinds of pressure. However, I am a professional programmer so my mentoring could be somewhat helpful for you.
If you are interested, please contact me on our discord server (or directly: alsoknown1).