Why does the "Output format" capture option not affect the file format?
In version 4.4.8 (v4.4.8-0-g0d289c003bfb), the final format of the packet capture file in the "Capture" --> "Options" --> "Output" tab depends on the suffix of the file name, and the two optional options for "Output format" (pcang|pcap) are invalid.
Just tested with Wireshark-4.4.8 on MacOS (ARM). I can not find an issue. What OS are you on? And can you provide the exact steps to reproduce the issue you are facing?
How are you determining what the file format is? Some file chooser dialogs on some OSes, and other things, will only use a file extension when claiming what a file format is. E.g., I can use Wireshark-4.4.8 and, select "pcap" as the output format but give it a "pcapng" extension, and various OS dialogs will claim it is a pcapng, but it is actually a pcap, as "View->Reload as File Format/Capture", captype, capinfos, or other tools will reveal. Also vice versa.