Correction: you cannot get fired ("Entlassung") without any reason in Austria, you need rather strong reasons to fire somebody[0], but your employment contract can be terminated with a notice period anytime* ("Kündigung")[1]. The notice period is 6 weeks at minimum by law (6-12 weeks is common in startups by employment contract) and includes "Postensuchtage"[2], which allow you to use 20% of your time during the notice period however you want.
*: every 1st or 15th of the month is common
[0]: https://www.usp.gv.at/en/mitarbeiter/beendigung-arbeitsverha...
[1]: https://www.usp.gv.at/en/mitarbeiter/beendigung-arbeitsverha...
[2]: https://www.wko.at/service/arbeitsrecht-sozialrecht/Anspruch...