https://www.youtube.com/watch?v=f4Q1cp0S964
(~14 min)

This guide works with the original CD (which is recommended) as well as the image file from the GOG-version.

Pastebin with the DOSBox Settings used: https://pastebin.com/yBwwPmis

For the GOG image file you gotta do one additional step:

Locate the .bin/.cue files in the install directory:

...X-COM Apocalypse\CD\

Use a programme such as "WinBin2Iso" to convert the .bin/.cue into an .iso.

That .iso can now be mounted by Windows 10 by simply double-clicking it.

DosBox is a virtual machine. Windows 8+ image mounter app not related to dosbox.

bin+cue is a bad format indeed. Iso as well.
You can just rename bin to iso or better img, no additional downloading required. At least img (and bin) created in Alcohol is identical to bin created by some else soft (discimagecreator). So renaming is ok in that case. Moreover, it also work same for many else disc images. usually you can rename lareger file to iso or better to img and image still work.

Windows image mounter app is WRONG choose to mount image. ESPECIALLY for DosBox. Mount it directly.
Same for most of the such applciations (wincdemu). They do NOT mount it properly. Especiialy with DOS filesystem on it.

Yes, some tweaks required in conf files for every games. Non DosBox, non GOG default conf files are good as general default settings.
And no matter what in there, you always should set cycles manually. Mmm... keep it auto, but reduce "steps" and use hot-keys for it during gameplay if game speed is wrong. And X-com is a example when you need adjust it during gameplay, global and battle mode work differ on same cycles (too fast globe time issue).

What are the reason for not recommending imgmount, and recommend Windows-crap-apps over it? You know you can get wrongly named files on that mounted CD (this is why even "_" not a good symbol for path, no spaces and no them - only "-")? In Wndows, and then in DosBox.
All such apps except SPTD-based Alcohol and DT mount it as a virtual catalog, not virtual drive. Its basically same as copy-paste files to harddrive. Same issues can happen as by copying it.
And DOS filesystem add additional issues.

Also as i understand you have wrong resolution settings. But you record it in windowed, right? And for windwed you set correct 4:3.

Its always some features onoriginal editions CDs. Maybe its should be recommended. And GOG as easier to get.
But fir easier to get GOG you dont need anything special. Just manyally edit conf file, for some options. Depand what ones available in GOG Launcher, they missed something sometimes randomly.
Keep 4:3. reduce cycles steps. Most of the optional set by DosBox and GOG launcher are OK.

For some releases better download DosBox from of.site. For some ripped releses WIN exe is missing. X-com1 is example (steam have it). And X-com1 is example where Win version is hugely updated than DOS one and have less bugs. Even on same edition cd. For such ripped releases here if possible better download source-ports mods and more better - original CD.
or mount provided GOG CD. It probably have Win content that can be overripted above installation.
This is anything i can comment here.
At the end of the video game working, image properly scaled. Which ones version better and else i dont have idea. But windows mounting and iso format - never be a good way.

I have done a lot of testing over the years and my method will work the best for X-COM Apocalypse.

These settings and the setup will give you:

- Best ingame performance, fluent even with lots of explosions and smoke.

- Perfect Pixel output on Full HD, WQHD, 4K and 5K, in windowed and fullscreen mode.
(While on WQHD and 5K you can enjoy it filling the whole screen, as 480p scales into it perfectly)

- Less frequent errors / bugs encountered ingame.
(i.e. "Please Insert CD" probability reduced A LOT)

- A working Learning AI. Due to the way the files are installed and copied, the game checks the installed files first and you may enjoy a finally working Learning AI.
(however it breaks when you save and reload the game or do things like Stun Raids...)

Resolutions are correct, if you choose 1920x960 fullscreen on a full HD monitor (1920x1080) the game will be in the middle as 1280x960, pixel perfect and sharp with black borders around. (as you can see at the end of the video)

The integrated image mounting function of DOSBox is horrible and will lead to errors ingame, including a more frequent "Please Insert CD"-bug.

However, when you mount only "d:\" (with the original CD) or for example only "e:\" (the drive letter Windows gives the mounted .iso) those errors frequency is reduced by a lot.

DOSBox itself doesn't care about the name of the ".iso", once it is mounted as a cd drive it will handle it correctly inside its DOS environment. It's just the integrated direct mounting system of ".iso"'s is horrible in DOSBox.

i talk about file system file naming. it can be coruupted if mounted by some wincde-windows-etc. Linux tools as well. Yes, iso if better for linux, but there is no proper tools to mount it as DOS filesystem disc.

< as 480p scales into it perfectly >
to another 4:3. you have back bard on video - and that correct. As i understand dosbox work in wodnowed on your example video - that why it have black bars. You set on thoose conf file correct 4:3 resolution for windowed. But set incorrect 16:9 for fullscreen. normal fullscreen = 4:3, as a termin. Widescreen is not a fullscreen term.
It nver be properly scaled -> wrong proportions and more smoothed image.

resolution itself not matter there. Just 4:3.

Your english is not good enough to understand.

All resolutions are correct.

Nothing will get streched.