Is there a way to share apps between user accounts?

Hello all, I'm a recent (as in, last week) PC user, converted from using Apple products for the past 15 years. I am...having a trying time understanding how some things work in the Windows 11 ecosystem that seem to not work as intuitively as they do on Apple devices. I know that's part of the trade off between the two systems, endless customization options vs streamlined user experience, and I'm determined to figure it out. The problem I'm having is that I have my account, where I've downloaded a bunch of apps I use regularly and have started setting them up, however my girlfriend created an account for herself a few days ago and...most (but frustratingly not all) the apps I've downloaded are not available on her account. Conversely, apps that she has downloaded are on her account, but not on mine. I assume this is common and well known, but it is nearly impossible to find a definitive answer online. So I have a list of questions.

1. Is there a simple way to simply make every app that exists on the computer available for both accounts to use and for those apps to show up easily in the Start Menu? Both accounts are administrators.
2. If not, can I make a folder in a certain location in which both of us can direct any apps we download to install into, and make this file sharable between the two of us?
3. Is there any obvious reason why some apps that I downloaded show up on her account, but not all?

I can only assume this is the most painfully basic question, but I am having no luck in solving it. Conflicting advice online, half the questions I find aren't exactly mine (like a common one I see is about sharing apps between "devices", I do not care about devices, I am not trying to share apps between devices I am trying to use downloaded apps on two different accounts), it's all adding up to an extremely frustrating time. The answer surely can't simply be that every app needs to be downloaded multiple times, one for each separate user account setup, right? My girlfriend seems to think that, even though the app needs to be installed on however many different user accounts there are, the actual app file won't duplicate. But that leads me to another question:

4. I downloaded Epic Games, signed in to my account and downloaded Genshin Impact (don't judge) which was 20GB+. Then my girlfriend signed into her Windows user account, had to download Epic Games again, tried to play Genshin Impact (which she has already purchased or whatever under her Epic Games account) and it wants to download the entire 20GB+ file again. What? That is insane. I'll need to buy new hard drives every month at that rate. What am I missing here?

Whoever makes it this far, thank you for putting up with my ineptitude. I don't mean to be a luddite but I am when it comes to the Windows ecosystem. But I'm trying to figure it out! Any help would be massively appreciated. Thanks

When an app is installed, there is an option to make that app available to everyone or only to that account. If you select the former, all accounts will then see the app.

What you can do now is go into the other accounts and ensure the apps are listed under All Apps. If they are, you can add a shortcut to the desktop for each app for each account.

There may be some more elegant way to do that -- so I defer to others about that.