Computer Configuration > Administrative Templates > Microsoft Edge > Sleeping tabs settings
Both
HKLM\Software\Policies\Microsoft\Edge
Setting this policy enables inactive (sleeping) tabs to be automatically discarded after 1.5 days of inactivity. This is done to save memory. When the user switches back to a discarded tab, the tab will need to be reloaded. If the 'SleepingTabsEnabled' (Configure sleeping tabs) policy is enabled, then this feature will be enabled by default. If the 'SleepingTabsEnabled' is disabled, then this feature will be disabled by default and cannot be enabled. If enabled, idle background tabs will be discarded after 1.5 days. If disabled, idle background tab will not be discarded after 1.5 days. Tabs can still be discarded for other reasons if this policy is disabled.