Pop mail accounts can only get access to and download emails from the server Inbox. This is the same for any email client, it's not a Thunderbird quirk, it's just how Pop mail accounts work.

You would need to logon to your webmail account via a browser and move those 'junk' emails into the 'Inbox'. Then in Thunderbird click on 'Get Messages' and it should download them. You may need to see if there is some setting in Outlook.com webmail account to stop auto marking emails as junk.

I believe Outlook.com needs the email addresses to be in the webmail safe senders list or contacts list to ensure it is not marked as junk and auto moved out of Inbox into Junk.

Info at this link may also help: https://www.wintips.org/how-to-disable-junk-email-filter-in-outlook-com-and-office365-web-app/

The Junk mail filter at outlokk.com cannot be turned off and takes precedence over any custom rule. The messages deemed to be SPAM by Microsoft are automatically sent to the Junk mail folder. The Junk mail folder cannot be removed.

The Outlook.com help forums have plenty of complaints that people are missing important emails deemed as junk by outlook.com and asked for an option to switch off the default junk filtering, but I think it fell on deaf ears.

Did you create a rule when received message is sent to your email address move to Inbox?

No pop accounts can access anything other than Inbox; Imap account would allow you to see the Junk folder.

I did create a rule to redirect all messages to my Inbox, but this did not work. All incoming messages are automatically filtered and dispatched to my Inbox or to my Junk folder depending on how the MS algorithm identifies the messages as “safe” or “junk”. I tried to create rules that would contradict some of the mistaken identifications made by MS. To no avail. I asked a MS forum about this. They told me that their junk filter takes precedence over any rule that I might create. So I have to accept that my Junk folder is always a mix of SPAM, PHISHING, and genuinely safe messages. This is not all. When outlook.com detects that a message header or text contains the words SUBSCRIBE, SUBSCRIPTION, or something related, they automatically include the sender and the alleged subscription in a list of subscriptions I am supposed to have made. But, like so many, I receive tons of messages purporting to have been sent because I subscribed to some newsletter. These messages are sent by hookers and the like phishing for a “date” or “friendly chat”. Even though I never subscribed to such newsletters, outlook.com systematically lists them in the “Subscriptions” folder, with a unique button allowing me to “unsubscribe” from each of these “subscriptions”. If I am foolish enough to unsubscribe, I am automatically sent to a phishing site. People have complained about this for more than a year. To no avail up to now…

You will need to use IMAP as your mail system, not POP if you want access to the spam folder from within Thunderbird.