Yep, that's enabled. I ended up finding a folder on my computer called "Magix Downloads" in my documents folder and thankfully still had the build 146 installer still there. I got lucky, but there should be a way for people to download older versions.

Unfortunately MAGIX can now make available only the latest builds of the two latest versions. Users are advised to keep installers of previous builds of those versions in case they have to go back to a previous build.

Where can we access these older versions? I couldn't find them online at all.

As I said the older builds of two latest versions are no longer available from MAGIX. See also this post for what is currently available. See also item 6 here for various update histories.

Magix really should have these all available in the "My Account"/"Service Center". I'm sure back in the day you could go back and get basically every version (that may have been before Magix took over). Relying on a volunteer to update a 4-year-old forum post just isn't enough.

@LukeT actually you can rely on that forum moderator. The update history is longer than the arm of the law. (First created a couple of months into the MAGIX era, i.e. 11/26/2016 and latest update 11/5/2020.)

You need to Ask Support if they are able to give you the reasons for the disappearance of those build links from MAGIX servers. This change happened early November 2020, not when MAGiX acquired SCS products in mid-2016.

Even better is to save it yourself to a location.
Before installing every version and build has to be downloaded to your used hardware. Since Magix it is always automatically in your documents/Magix downloader/ Installationsmanager from where you can save it at all places that you wish.

@j-v wrote

Even better is to save it yourself to a location.

+100. As I said earlier as well, keep the installers. It has been recommended to keep them at least until you are sure the new build works as expected since I joined this forum almost 10 years ago, probably earlier as well.