I do not think that any journal would guarantee a decision within a month; it might take a month to find a referee. Sometimes, a journal will give its editors the freedom to summarily reject a paper that they find wanting, and that can certainly happen in less than a month.
The quickest reputable journal I know of is Proceedings of the National Academy of Sciences (USA). Their website guarantees a decision within 7 weeks. But papers submitted there must be fairly short and of very broad interest. The vast majority of papers submitted there are rejected.
For more traditional journals, be prepared for a minimum wait of 6 months. Also, note that a referee who agrees to review your paper might be adversely affected by the pandemic, which might affect the turnaround time.