If Nokia 3310 is too old, how about the other brand which had launched classic phone without Android system?
Such phones have very weak SoCs and low RAM, so modern OS-es such as Android or Lineage can not be installed. Their boot-loaders are probably locked, so I doubt you can change anything. Even if you could, it would run so slow, it would be unusable.
So, having a preinstall Android is the minimum requirement to ensure such LineageOS also work fine?
Sorry I haven’t try to install LineageOS, it need to root the phone and the existing Android system would be destroyed or hided? Would it downgrades the Security(e.g Android provide Encryption to secure the phone)
There is an official list of supported devices: https://wiki.lineageos.org/devices/ Just use a device that is on this list. There may be unofficial LOS versions for your device, but as people usually don’t trust software from unknown third parties, you may not want to install unofficial LOS ROMs.
By installing LineageOS, you replace the stock Android of your phone with LineageOS. So the stock Android isn’t there anymore.
It depends. Some stock security features may be missing while other controls could be added.
Quoting an answer from our last AMA event:
“Is my LineageOS device secure?”
There is also no binary answer to this. In your typical smartphone are lots of different hardware chips. They run their own firmware (e.g., cellular baseband, cellular RF receiver, Bluetooth, WLAN, GPS, SIM card, SD card, screen, power supply). Your smartphone operating system like Android or iOS runs on top of this, using its dedicated application processor. As always, software may contain security vulnerabilities, and migrating from Android to LOS doesn’t fix security vulnerabilities in your WLAN chip, for example. Besides, all current standards for mobile connectivity (3G, 4G, 5G) come with weaknesses, Bluetooth includes vulnerabilities, and WPA (securing your WLAN) contains flaws.
So if you look at smartphone security, you need to consider that there isn’t only the user operating system (like Android or iOS) but many more hardware and firmware involved, e.g., see https://arstechnica.com/information-technology/2020/08/snapdragon-chip-flaws-put-1-billion-android-phones-at-risk-of-data-theft/.