Help me understand Google's Project Treble & Project Mainline please.

As far as I can summarize from reading how the various operating systems
update (all of which update completely differently), Treble is modularizing
how the manufacturer pushes out updates and Mainline is pushing a few dozen
core Android OS updates directly out of Google Play (bypassing the OEM).

Essentially Android is unbundling system level apps and services from the
operating system so both can be updated regularly and universally
but with the system level apps updated directly through the Play Store.

These seem to be the fundamental core components in the current Android:
(a) The chips (made by the chip makers & assembled by the manufacturers)
(b) Low level firmware for those chips (maintained by the chip makers)
(c) The Vendor Interface (VI insulates everything below from that above)
(d) The Android CoreOS framework (Project Mainline's core Android modules)
(e) The Android Developer API (AndroidStudio codes for compatibility)
(f) The Compatibility Test Suite (CTS works across hardware ecosystems)
(g) Key Google & manufacturer apps (eg Google Pay & Samsung Pay)
(h) Android apps

As far as I can figure out this is the current list of core OS apps updated
in Google Play (all or at least most of which are open sourced AFAIK).
1- adbd com.google.android.adbd (APEX)
2- Android Neural Network API Runtime com.google.android.neuralnetworks (APEX)
3- Captive Portal Login com.google.android.captiveportallogin (APK)
4- Cell Broadcast com.google.android.cellbroadcast (APEX)
5- Conscrypt com.google.android.conscrypt (APEX)
6- DNS Resolver com.google.android.resolv (APEX)
7- Documents UI com.google.android.documentsui (APK)
8- ExtServices (APEX) com.google.android.extservices (APEX)
9- ExtServices (APK) com.google.android.ext.services (APK)
10- IPsec/IKEv2 Library com.google.android.ipsec (APEX)
11- Media Codecs com.google.android.media.swcodec (APEX)
12- Media Framework Components com.google.android.media (APEX)
13- Media Provider com.google.android.mediaprovider (APEX)
14- Module Metadata com.google.android.modulemetadata (APK)
15- Network Stack Components com.google.android.networkstack (APK)
16- Network Stack Permission Configuration com.google.android.networkstack.permissionconfig (APK)
17- Permission Controller (APEX) com.google.android.permission (APEX)
18- Permission Controller (APK) com.google.android.permissioncontroller (APK)
19- SDK Extensions com.google.android.sdkext (APEX)
20- Statsd com.google.android.os.statsd (APEX)
21- Telemetry Train Version Package com.google.mainline.telemetry (APK)
22- Tethering com.google.android.tethering (APEX)
23- Time Zone Data 2 com.google.android.tzdata2 (APEX)
24- Time Zone Data com.google.android.tzdata (APEX)
25- Wi-Fi3 com.google.android.wifi (APEX)
26- Android Runtime (APEX) converts Java bytecode to native machine code

But even the low level firmware from chip makers is now integrated in Google Play
https://www.androidauthority.com/gpu-driver-updates-phones-1096423/

There are too many key Google & manufacturer apps to list but here are
examples of some of the Google apps that are in the "key apps" category
27- Android Auto
28- Contacts
29- Files by Google
30- Find My Device
31- Gboard
32- GMail
33- Google
34- Google Assistant
35- Google Calendar
36- Google Chrome
37- Google Docs
38- Google Drive
39- Google Maps
40- Google Pay
41- Google Play
42- Google Play Music
43- Google Text-to-Speech
44- Messages
45- YouTube
(this list of key Google apps might go on for a while)

And then there are the key manufacturer apps specific to each OEM
(46) Samsung apps https://www.digitaltrends.com/mobile/best-made-for-samsung-apps/
(47) Motorola apps https://play.google.com/store/apps/developer?id=Motorola+Mobility+LLC
(48) OnePlus apps https://play.google.com/store/apps/details?id=com.oneplus.mall
(49) LG apps https://play.google.com/store/apps/developer?id=LG+Electronics,+Inc
(50) HTC apps https://play.google.com/store/apps/developer?id=HTC+Corporation
(too many to list)

As far as I can tell almost everything on Android above is updated
constantly, and while some of what is above is updated for 4 years
https://9to5google.com/2020/12/16/android-updates-4-years/

Much of what is above is updated "forever" (where that's defined as
they do not plan at this point to stop updating it which means that
it can be replaced or dropped over time but the market dictates that).

My two main questions to ask of you are how is the Google Play update done?
Do they ASK us to update or do they update these core OS components automatically?

And my second question to ask of you is which of the components above
have a planned EOL date?