You probably mean the system apps that have an icon in the launcher? (I do not think that you have uninstalled e.g. the system app com.android.bluetooth because then Bluetooth would simply not work 
)
My list of system apps on /e/OS U (names may unfortunately differ on /e/OS T):
- App Lounge:
foundation.e.apps - Tasks:
foundation.e.tasks - Bliss Weather:
foundation.e.blissweather - Browser:
foundation.e.browser - Files:
com.android.documentsui - Settings:
com.android.settings - Gallery:
org.lineageos.glimpse - Calendar:
foundation.e.calendar - Camera:
foundation.e.camera - Contacts:
com.android.contacts - Mail:
foundation.e.mail(based on an older version of K9 Mail, no Material You yet?) - Maps:
com.generalmagic.magicearth - microG settings:
com.google.android.gms - Music:
org.lineageos.eleven - Messages (SMS):
foundation.e.message - Notes:
foundation.e.notes - Open Keychain:
org.sufficientlysecure.keychain - Calculator:
com.android.calculator2 - Recorder:
org.lineageos.recorder - Phone:
com.android.dialer - Clock:
com.android.deskclock
Personally, I would hesitate to deactivate any of these apps and simply not use them if I do not like them. There may always be unintended side effects; moreover, the system apps can work as a fallback if one of the apps installed instead has an issue (for instance, Fossify Phone may currently have some problems with emergency calls like 911 or 112, see Emergency calls (110 or 112) are not working (well) · Issue #250 · FossifyOrg/Phone · GitHub)