MacBook Pro 2018 - Cannot install Mac OS Catalina after having deleted all files on the internal SSD (potentially T2 chip issue)

Hello community,

I have a problem with installing MacOS Catalina on my new MacBook Pro 13" (2018 model). After browsing the internet for quite some time and trying to solve the problem myself, I have to admit that I problably won't be able to do so on my own.

Maybe the community can help me:

I just recently bought a new MacBook Pro 13" (2018 model). In order to have it checked by a local retailer (not an Apple store, but an authorized reseller) for a potential screen flickering issue (different topic...), I deleted all the files on the laptop using the MacOS tools. For this purpose, the internal SSD was erased entirely, inclung the operating system (Mac OS Mojave).

From my previous experience with other MacBooks (including a MacBook Air 2012 and a MacBook Pro 2006), I know that this is a safe way to do it, since - to my knowledge - installing the OS via an external harddrive could easily be accomplished even after having erased the internal harddrive/SSD entirely.

I picked up the laptop yesterday and tried to install Mac OS Catalania via an external SSD (since no operating system is installed on the laptop). I succesfully created a bootable installer, but the installation won't work (I have tried all the shortcurts and commands listed on the relevant Apple websites). No matter what I do, the laptop starts, then shows the rotating globe - and that's it. The installation doesn't start nor can I chose other options after having chosen a WiFi connection.

Starting the laptop using the shortcut Option+R, the laptop shows the external SSD and the option to install Mac OS Calatina. However, when I try to start the installation, the laptop will only show the rotating globe again and nothing happens.

By now, I have learned that this probably has to do with the MacBook Pro's T2 chip. Unfortunately, I haven't heard about this before I deleted the internal SSD. Consequently, I have not disabled the security feature that prevents the MacBook from booting from an external SSD/drive. That seems to be the issue right now preventing an installation via the external SSD.

It seems like I am stuck now. I have no way to access any disk utility or similar programm/app - at least not to my knowledge.

I would really appreciate it if someone from the community or Apple can offer a workaround. What are my options here?

Many thanks in advance!

mcfly_2nd