I’m been using HOS for 2 years with no major problems. I have some add-ons, such as File Browser. In the last three weeks: File Browser has disappeared; I do not have Settings->Add-Ons; nor do I have Settings->App. The Installation method now shows “Home Assistant Container” with core 2026.1.2 and frontend 209260107.2. I have not done anything to change the system other than applying updates as they are available. I know it seems crazy, but it seems that HA changed from HOS to HA Container. Is this possible, or am I missing something?
No addons with container Install
You much manually Install the docker container for the service that was previously installed as an addon
Add-ons or apps will not work in container install. You need to load your stuff manually with Docker containers and maintain them yourself. Welcom to the harder way to do stuff.
Is HOS something different than a typo for HAOS and there is a reason why the user lost his addon store without any steps from his side?
Or did both of you answer without reading the start post?
This is irritating to me. 
I read it like he installed HAOS and after some updates his installation got confused and identified itself as a container installation instead of the HAOS type it has been.
No idea how that happened, but starting to try to use the underlying OS as docker engine and install additional plan containers wouldn’t look like a good idea to me in this case. 
But most likely I miss a part of the puzzle in here and have the chance to learn something. 