Some highly committed LineageOS developers surprised us all with an Android 10 port for the Samsung Galaxy S2 and Galaxy Note 3. If you're still holding on to yours, here's how you go about installing it on your device. The steps remain the same for the Galaxy S2 and Note 3, and I'll mention each device specifically.
Step 1: Download ODIN v3.07 using this link, and then run it
Step 2: Boot your phone into download mode by pressing down and holding the Volume down + Power/Standby + Home for 10 seconds.
Step 3: Connect your phone via USB to your PC, and volume up on your phone. ODIN should detect your phone.
Step 4: Download the following files that we'll need for ODIN later.
i9100-LOS-16.0-Emulated-Storage.pit (this goes in the PIT tab)
i9100-LOS-16.0-Emulated-Storage-TWRP-3.3.1-1.tar.md5 (this goes in the PDA tab)
lineage-17.0-20191220-UNOFFICIAL-i9100.zip (this is the actual Android 10 build for the Galaxy S2)
There are four different builds for the Galaxy Note 10. Go to Settings > About phone to determine the model number of your phone and download the corresponding build.
Once you've downloaded the software corresponding to your phone, don't forget to download GApps (ARM64, Android 10, Pico) and make sure to copy both onto the phone's internal storage. In this tutorial, we'll use TWRP to install the build onto the device directly. You can use ADB sideload too.
Step 5: Populate the PIT and PDA tabs with the files mentioned above. ODIN should then look something like this. Note that I don't have a phone connected, so yours will look a bit different.
Step 6: Before proceeding, be sure to uncheck the Auto-reboot button. Leave everything else as it is.
Step 7: Press the start button and wait for the process to complete. Now, press and hold Volume up + Power/Standby + Home for 10 seconds.
Step 8: The phone will now boot into TWRP and will ask you if you want to allow it to make modifications. Follow the on-screen instructions and now you'll be greeted by the following screen.
Step 9: Before installing anything, we'll need to wipe the device. Tap on Wipe, and you'll be greeted by the following screen.
Step 10: Tap on Advanced Wipe and check all the following boxes.
Step 11: Swipe the area of the screen that says 'Swipe to Wipe' and wait for the process to complete.
Step 12: You'll now be taken back to the TWRP main screen. From here you'll need to install the LineageOS build that you saved on your device's internal storage. Tap on Install and select the corresponding file from your phone's internal storage and tap on Install Image.
Step 13: Install the GApps package once LineageOS is installed successfully.
Step 14: Reboot your device and you should be running an unofficial Android 10 build on your Galaxy S2 or Galaxy Note 3. To prevent "Encryption unsuccessful" error of GAPPS at first start,
reboot to TWRP and Wipe -> Format Data .
Galaxy Note 3 users shouldn't have much of a problem as most of the features appear to be working normally. The Galaxy S2 build has been deemed as 'unstable' and not suitable for daily use. You can find out more about the bugs and report any you find on the official XDA Developers forums thread for the Galaxy S2 and Galaxy Note 3.