what exactly are you looking for? there are many guides for switching to linux, for example, arch wiki; has enough details for anybody. similarly, there are other distro wikis (fedora/debian/mint/…). But none of them are specifically for switching from windows (10). Most of them do mention that backup your stuff, or mount windows partitions for moving stuff.

If you need something to switch specifically from windows, that is hard. because the way people use windows changes a lot with people. My personal recommendation would be to just search “switch to linux” on youtube, find suitable videos (in prefered languages or target audiences, which are also suitabbly licensed(most linux youtubers release their stuff under some variation of cc, and youtube by default has also some cc license for all videos. you can check about licenses in youtube description.)). Video demos for people today or more approachable, and can also help navigate any issues that might occur during the move. Once they have some distro installed, they can look up distro wikis to build upon.

one could just soak this in water for very long time, coat with clay from inside,and bake the clay, and get reasonably good fire protection. but $1500 is way to much, who do they think they are, apple?

I do not think it is a good idea to prepare a vm image and install it as iso. it can be done afaik, but not a great idea. Assuming he (your dad) already has a ubuntu system (presumably some lts, i am asssuming something like 1604, 1804 or 2004) then it is easier to just upgrade the system. I know you said that he has forgotten to upgrade, so i would ask him to somehow send you a photo of what he has installed right now (can be hard, but maybe just asking what animal is present on the wallpaper (if he uses the default one that ubuntu uses) can help. even look of top bar or icons can help to get the age. Afaik, ubuntu upgrade paths are relatively stable, so once you know what version he uses currently, then you can install that version, and upgrade it to newest install on your system and record instructions. This would be long and tedious task. I do not use ubuntu, so i do not know what jumps can be taken (i know you can jump from 1 lts to another, something like 1804 to 2004, but can you jump 2 lts versions? some ubuntu forum or wiki post can help regarding this). Once you complete upgrades, you can record instructions and send them.

This can be a easier for following reasons -

• he would not have to plug in usb and boot into installer mode - this can be hard if he does not know what key to press, or if he does not press it fast enough

• you would still be using some standard installation, rather than your “custom” iso - not a big thing, but upgrades are more certain in a standard installation

• ubuntu has snaps - I am not a big fan of snaps, but it is a good thing for likes of your dad, who would prefer to have there apps (like web browser) auto updated in background. Mint has flatpak, but by default stuff is installed as deb packages, upgrading them requires sudo password, which can be hard for your parent.

the virtual image is much larger than iso, because it is uncompressed. Isos are you compressed by something like squashfs, which prepares something like a tar or zip file, which is also mountable. Also your intial virtual file system allocated size might be larger (which would largely be empty, this would be “sparse” file). From my prior experience, you can sometimes have sparse file errors, which can cause errors at bootup, these can be benign, but may seem strange to your father.

Someone else mentioned, you can also possibly install it on a laptop, and then ship that to your father, or buy a prebuilt laptop with linux preinstalled. Nowadays, some big brands like hp/dell/lenovo also have options in there build configurators to select the operating systems, and there are also linux specific vendors (more expensive). But this option in general is expensive (because there is a laptop cost).

Also, where does your father live? If he lives somewhere maybe close to me or someone you know who can go and upgrade / install new system for him. This can be hard for logistaical reasons, or you may not be able to find someone trustworthy.

there are about 432 = 4! ways that is 24 and if it alarms after 3 tries, it can be safe-ish.