I have quite a few older Android devices, my main device runs 8(O) and I have some on 7(N), 6(M), 5(L). 4.1~4.4 support was already gone with Fenix, but now it seems like they got 5/6/7 as well. https://f-droid.org/en/packages/org.mozilla.fennec_fdroid/
Not usable for anything Internet-related really, but I still use Samsung Galaxy Ace with Android 2.3.6 as a secondary device. It lasts long enough in standby for me to just forget charging it.
But I got that refurbished on AliExpress. It seems to be reflashed with German version of stock ROM, but an odd thing is both have the same ID on ADB. Something along the lines of 1234567890ABCDEF.
The components… sometimes battery percentage just jumps down randomly, and the vibrator squeeks if not used for a while.