i do not have this model but have the previous 2 models, ua6800x and ue630x.
both are 4k smart TV with AndroidTV; former is 1 yr old, latter is 3.5 yrs old.

the al1x is almost the same as the ua6800x, the androidTV (android8) is exactly the same, so do read a bit of this longer thread:
https://forum.lowyat.net/topic/4488602

ue630x is an older model on android6, 4k non-HDR but has similar functions:
https://forum.lowyat.net/topic/3811168/+1600

there are comments floating around somewhere like "androidtv can't play after 2-3 years" or "androidtv is very sluggish".

androidtv is a specialized os from google; it doesn't die!
while the updates will cease after 2-3 years becos tv maker will not keep upgrading, the TV will keep working like any other TV.
say the TV today with android8 gets a last upgrade to android 9 in 1 yr,  the android will not be obsolete for another 4-5 years.
i have 8 year old android4 devices that are still working.
the TV itself is unaffected for normal functions of hdmi input like ps4, android box, DVD player, Astro...

about longevity, nobody has all the statistics but i find them very lasting.
last 10 years, i had a total of 5 sharps; one had slight bleeding after 8 years, the rest all still working good, never had warranty issues.

as for sluggish, i do not know other brands but sharp androidTV is NOT sluggish.

it is very useful to have androidTV if u already know how androids work, have use it on phones and tablets.
that way, u will easily get to know how to install apps and use it nicely.

Youtube, netflix are preinstalled apps, easy to use with just the remote control which has voice search function too.

i cannot comment the specifics of al1x since i am not using one.
do ask the owners in this thread to comment on specifics if u need.

lastly, dun forget this tv is a mid-range TV, try to compare with similar size and prices only.
always trust your eyes and wallet, not "expert reviews" by other people who had never used it!

I bought this unit after comparison between this model and Sony Android model and very much informative guidance from AVFAN.

So far so good, the Android OS is a notch advance compared with my Smart TV. You can install apk apps but do not expect all apps can be installed smoothly like in your phone as some will be blocked or not compatible with Android TV. However no regrets, the TV is decent and no lags, acceptable PQ and audio.

Honestly, I have not tried playing the mkv file with sub as nowadays I just stream the movies. Perhaps expert AVFAN can shed some light on this.

Reboot the TV.