I assume this is because sqliteonline is using the sqlite library, not running the literal sqlite command line application. Per item 7 in the faq (https://sqlite.org/faq.html), the way to get that info would be to run something like the following:

SELECT * FROM sqlite_schema WHERE type='table' ORDER BY name;

The website does seem to correctly return the names/schemas of whatever tables you've created if you run the command above, but the editor (incorrectly) adds red squigglies around the command, since I guess it doesn't realize this is allowed.

P2P “Share/Collaborate” mode: the UI text and toasts (“Share”, “Close connect”, “connected”, “No connected.”) plus e.rtc.user strongly suggest a feature where someone “hosts” a DB and others connect directly to run queries/see results live.