xiaomi already like this since their old era, i know it since mi 3

they never update android version, only miui version

my mi max 1, this phone launch in 2016 and xiaomi discontinue update on it on somewhere around 2019, so it's normal lor 2-3 years like that

xiaomi say they discontinue it based on user base count, small user base phone are very likely to get discontinue faster

my mi max 1 also lag and slow but luckily no bug

but i use it as spare phone for gps now, already upgraded to p30 pro during its launch

maybe you are not miui fan since the old miui 4

xiaomi never update the android version of the phone even when push out new miui

unless the phone is absolutely new and is flagship model, else you will rarely see android version is getting updated on the phone

this is how miui gain its user base back in the old time

usually those new features that come in new android version

they backport the features to make the features work base on miui version instead of android version

so even if the xiaomi phone running old android, but with latest miui, it will get the features

this is really uncommon practice from miui back then until now

bcoz that old time google rarely release android updates and difficult to port it to the customized android (miui), developer from that time will have a lot of works to do to port the updates and fix bugs that causes to the customized android (miui)

so miui stick to the base android version for that phone, then fix bug and add features on its own without relying on android updates

but now android updates getting better so story is slightly different but the base principle of miui is still the same