SLA tracking in DevOps

For the operational day-to-day/hour-by-hour activities I presume you're already using Board with columns representing your key workflow steps, and making liberal use of the Card Rules feature (available in settings) to make cards the criteria you mentioned standout. E.g. "Severity" (custom field) = Critical show as, say, Red; and so on. Consider having an "ambulance" Swimlane for special cases 😉

For the SLA reporting end, the Cumulative Flow diagram (available in the Board Analytics) could provide a quickest overview. (I typically take screenshot, paste into PPT and add synopsis comments on trends/anomalies/exceptions).
Regarding Dashboards, the Charts Widgets are particularly useful/powerful.  But for the kind of analysis/insights you mention I'd think I'd also be exporting the results set to Excel so that SLA meta-data can be used to color-code or report on met/not-met etc.   If/once that becomes a stable regular thing then I'd consider doing it using PowerBI.