[Sony Xperia 1 II Questions & Answers] WOLF33B:
if you mean porting the app only. then yes. it USED to be possible. back in android 11 era of 1 ii and 1iii. it is a 100% possible to update or add new app that available on 1 iii but never on 1 ii. i remember have all xperia 1 iii feature(software) in my xperia 1 ii devices just by check apkmirror on 3 sony developer name(not all app in Sony Mobile Communications Inc., some are actually under other sony same. and that important since sony like to make app as modular).

anyway fastforward if you install latest android 12 then it kinda impossible. or have cons and pros instead fully working. that due to *i think* sony know this and patched most of core app. went i said patch. is you cannot update system app anymore as sony add flag to almost all core app making it impossible to update without root. like i said before sony like to make app as modular. and went i said core is app that not added to your launcher nor it can open. this app normally work in background and with other app that you use. example is GE launcher. this app is using more than 5 app(if you think only 3 then you are wrong there subsystem and subsystem 2 to make the feature work. hidden stream app to use xperia steam devices. and usb app that allow this app to stream into capture card with configureable instead as is. at least it used to until it no longer possible on nonroot)

another app is camera. camera actually have many modular app to make it work, yes. you selfie, panorma are seperate app. not ony pro mode

but there a hope. kinda. i remember that early android 12 sony is not yet patch it. making you able to install early android 12 app from 1 iii and 1iv without problem(as long as you download the needed module app. including xperia service? if i was remember correctly many 1 iii app need newer xperia service to work properly without crash(or missing feature). the problem is i dont know what firmware is that. all i know it just the very early one instead mid to last update. the easy route would be downgrade to 11 then manually update until very fiest andorid 12 update then stop.

summary

if you willing to downgrade to early android 12(the one before patched). then yes you can just download all app you want from xperia 1 iii and even 1iv. just remember to check other sony dev name in apkmirror to download the some modular app. if you dont know. just trial and error then

if you not willing to downgrade. then there some app that work from 1 iii or 1iv(i have working 1iv video pro will high quality stabilizer enable. or far better one went zooming. and stream. with cons that it can crash if you try use hardware feature that not present in 1ii like 120fps on lower resolution and subject tracking)but remember since core app is on older or not present on your devices. there always a missing feature or straight crash it until you delete user data.

some app i tested or daily drive in non official version(unofficial update)

-camera app(no effect but no crash) >unkown xperia

-potrait selfie(no effect also no crash) >unkown xperia

-pro mode(no traking. no ai zoom. new adjustable menu, new basic mode. can crash but only if you really "bang it with hammer" for daily drive it stable) > xperia 1 iii

-video pro(high quality stabilize, vertical mode. stream mode. more setting, raw 120fps hdr/non hdr video, can crash on few setting. trial and error the setting and just dont use it) >1 iv

-GE launcher+module(the ui is more modern. can stream until overheat, some feature missing or not work due to missing subsystem,subsystem2,stream(from xperia stream). stable enough for daily drive) > 1 iv

-panorama(no effect but no crash) >unkown xperia

-multi-window switch(no effect, never crash but could be, due to missing newer xperia services) > 1III

-cinema pro(can be updated but i think it have no effect and actually lose some feature, not recommended but no crash) > unkown xperia

-creative effect(no effect but no crash) > unkown xperia

-xperia services(can be update but cause crash / not responding due to missing something) > possible from 1 iii. broken from 1 iv

-dolby atmos(can be updated. but make dolby broken. the ui is new but all feature is not working) >unkown xperia

-external monitor(might unresponsive sometimes if the display input suddenly disconnect/corrupt. and need restart to detect again. but as long as you not touch the usb type c then no problem. stable from daildrive and have record/stream. multiple new menu all feature work as intended) > xperia pro-i(recommended due to have more feature) or xperia 1iv

-endurance mode(can be installed. but cannot be trigger from supported app like game or external monitor?. basically do nothing) > unkown xperia

-dynamic vibration(no effect but no crash) >unkown xperia

-info app(use non sytem info app make all info app widget to be locked/un usable. and opening info app will promt qr code to the information of the smartphone info app you use. basically render is useless. but any info app is possible to be install)

-sony album(older:working as you older xperia(layout geo map view, sound photo etc except went the unkown format like 120fps hdr is open. then it crash, new:working just like lasted album from older experia except same thing. and missing feature like geo map view)

-music pro beta(working fine but online feature wont work since login and subcribe plan broken. but for record it work with no problem at all) >xperia 1iv(spesific version only. some version have some kind of lock thing that make it unlaunchable on non xperia 1iv, to use this version you can just create activity shorcut to launcher to main menu instead default one but version 1.1.0.b.0.14 will out of the box)

-3d creator(work fine. all offline feature avaiable. all online already stop working enable dev menu would allow extended feature like flashlight etc) > unkown xperia

-support app(you can but why? no new effect no crash)>unkown xperia

-weather(working as intended. no problem. even if it designed for 16:9 it work great on 21:9 xperia) > unkown xperia

-xperia view(working fine. all vr and advertise feature work great. could be configure to work with non xperia view vr headset. but beware. on xperia 1ii or my display went enter vr mode i think my display flickerring. could be due to it trying to run in 8k 120hz mode?. in non vr mode everything work great.