My inbox has now been split into Focus and Other.

Refer to https://support.microsoft.com/en-us/office/focused-inbox-for-outlook-f445ad7f-02f4-4294-a82e-71d8964e3978

Focused Inbox separates your inbox into two tabs—Focused and Other. Your most important email messages are on the Focused tab while the rest remain easily accessible—but out of the way—on the Other tab. 

To create an inbox that "feels right" to you, the system takes into account emails and contacts with whom you interact, and filters out noisy sources like automatically generated or bulk email. The more you use it, the better it gets.

Select the version that corresponds to the one you are using and follow directions to configure it

If the above response helps answer your question, remember to "Accept Answer" so that others in the community facing similar issues can easily find the solution. Your contribution is highly appreciated.

hth

Marcin