Can I apply for both unfair dismissal and general protections?
Generally, no. The Fair Work Commission's guidance treats them as mutually exclusive once one application about the dismissal has been lodged.
The Fair Work Commission's own guidance answers this directly, in the list of things you should know before applying for general protections: "You cannot apply if you have already made another application. For example, if you have already made an unfair dismissal application or an application under anti-discrimination laws about your dismissal."
Why this makes the choice worth making early
Because both claim types run on the same 21-day deadline, and because lodging one generally closes off the other, the decision about which claim actually fits your situation, covered on the unfair dismissal vs general protections guide, is not something to leave until later in the 21 days. Once an application is lodged, this site has not sourced whether or how it can be withdrawn and replaced with the other type within the same window, and does not state that it can.
What the two claims actually ask
The reason the Commission treats them as exclusive is that they ask different questions about the same event. An unfair dismissal claim asks whether the dismissal itself was harsh, unjust or unreasonable, weighing factors like whether there was a valid reason and whether you got a fair process. A general protections claim asks whether you were dismissed for a reason the law specifically prohibits, such as exercising a workplace right. A dismissal can, in principle, fail one test and not the other, which is exactly why working out which one actually fits your facts, before the 21 days run out, matters more than picking whichever application form looks familiar.
If you are not sure which one fits
Reading both explanations side by side, the unfair dismissal vs general protections guide and the general protections coverage guide, before lodging either application is worth the time it costs inside the 21 days. This site cannot tell you which claim fits your specific dismissal; a lawyer who has seen your facts can.