Currently Microsoft works with different PGs on recommended alerts. Mostly focusing on compute resources first (virtual machines, AKS clusters).
Each product group has own recommendations or guidance what to monitor. Following the Microsoft Learn.
Azure SQL - https://video2.skills-academy.com/en-us/azure/azure-sql/database/monitoring-sql-database-azure-monitor?view=azuresql
NSG flow logs - https://video2.skills-academy.com/en-us/azure/network-watcher/network-watcher-nsg-flow-logging-overview
AppInsights - it's a monitoring tool itself
Azure AD usually is being monitored for security stuff - https://video2.skills-academy.com/en-us/azure/active-directory/reports-monitoring/concept-sign-ins