Can it open a password-protected ZIP?
It can list what is inside one (names, sizes and which protection is used) because a ZIP's index is not encrypted. It cannot open the contents: neither ZipCrypto nor AES is decrypted here, which is why you are never asked for a password. If you know the password, 7-Zip, Keka, WinRAR and Windows Explorer will open the archive with it.
Why is there no password field?
Because there is nothing this page could do with the password you typed. The engine that inflates bytes here decrypts neither ZipCrypto nor AES, and a field that is guaranteed to fail is less honest than saying so up front. No password field also means there is nowhere for a password to go.
Why are the filenames gibberish?
The archive is old enough that it does not record which character set its names use, so they have to be guessed. Pick the encoding that matches where the file came from: the list re-reads instantly, because names come from the index and nothing is decompressed to show them.
How big an archive can I open?
It depends on the device, because the archive is held in memory whole rather than streamed: 256 MB per archive and 192 MB per unpacked entry on a desktop, 64 MB and 48 MB on a phone or low-memory laptop. The figure for your device is printed on the page, and an entry over the limit is refused before it is attempted, with the reason.
Does it open RAR or 7z?
No. ZIP only. Supporting 7z or RAR would mean shipping a multi-megabyte decoder for formats this page does not promise. Inside a ZIP, only Store and Deflate are extracted; BZip2, LZMA, Zstandard and PPMd entries are listed but cannot be unpacked.
Is my archive uploaded?
No. Your browser opens it from your disk; no part of the archive, and no extracted file, is sent anywhere. People routinely hand archives full of customer data, configs and key files to upload sites. That is exactly the transaction this page avoids.