That falls under Options > Privacy & Security > Logins and Passwords > “Use a master password”.
EDIT: Interestingly, support.mozilla.org apparently (!?) has less information than what some have volunteered at: “How does Firefox encrypt passwords without selecting Master Password?”
Although that had been discussed almost 5 years ago, so definitely prior to Firefox Lockwise being utilized. It’s a bit disappointing that all of the jibber-jabber on Mozilla support wouldn’t have the basic information one would be looking for… Although I must confess that I cannot look at their white backgrounds there, which can’t be styled (or, I don’t know how to) and therefore I’ve only scanned through some info very quickly before having to dump those tabs.
(Not even something like the Dark Reader WebExtension is able to tame the page backgrounds there, don’t know if it’s possible via some config, or perhaps only with using Stylish, or not at all; it’s a shame Mozilla will not allow us to read the documentation in peace.)