I have a website running on typo3 version 10. I want to do an upgrade to version 12, but I'm struggling on where to start. There is no composer package installed on the machine, so I guess typo3 was installed in legacy mode, and I also have a bunch of extensions installed on the system, some of them are from the TER and some of them are custom extensions. The documentation (and what I could find online) is not very clear. Is there a clear and detailed step by step strategy on how to do this update?
I have tried running the extensions checker, but this somehow seems to freeze after analyzing the first few extensions, also the website crashes when I do this and is not accessible anymore