You need to check what the Mac OS version is on your machine, when it is 10.13.6 or lower, you can't upgrade Logic to 10.5,
even though you see the Logic Update button, which should NOT show because it is a bug in Mac OS.
When you have an older machine it could be that it is up-to-date (within a specific version range like Mac OS 10.12 (Sierra), 10.13 (High Sierra) etc.) but it does not support later versions of Mac OS (i.e. 10.14, 10.15 and up).
I for example have an older iMac and it does not support a higher Mac OS version than 10.13.x - so it is up-to-date but only until the latest 10.13 version, which is 10.13.6 (so not the available higher Mac OS' 10.14.x or 10.15.x - since it is not compatible with that).
On the other hand I have a newer Macbook Pro which supports 10.14 and higher. On that computer I can upgrade Logic to 10.5.
This means you're either stuck with an older machine which does not support some higher Mac OS versions or your machine does support it and you need to upgrade to 10.14 or higher.
A very useful overview of Mac models and supported OS can be found here: https://eshop.macsales.com/guides/Mac_OS_X_Compatibility
Hope this helps.
EDIT
@Jaro876: sorry missed your message before your last one.
When you have Mac OS 10.15.2 installed Logic should upgrade indeed I persume.