QWERTZ keyboard, ‘At’ (@) in G key

I bought my MacBook Pro in 2017, which came with a Swiss keyboard (QWERTZ) as follows:

A couple of weeks ago my laptop crashed and I took it to the nearest Apple shop (as soon as they re-opened during COVID19 de-confinement).

I collected my laptop today, which is now repaired (software issue), and when reconnecting at home I was asked to set up my MAC.

The first ‘setup’ question is ‘Location’, which is when we basically chose our keyboard setting.

So I chose ‘Switzerland’ thinking I would get my old Swiss keyboard back.

I did set the QWERTZ keyboard except that in the subsequent setup steps, when entering my email address, I could not find the "AT" sign (@) which on the physical keyboard is printed on the G key, as shown in the picture above.

I then found out that ‘@‘ appeared by clicking the right-ALT key plus ‘L’ which clearly is not where it should be.

To make things worse, because my password includes some symbols, I tried it first where I could see all characters (under email address), and to my horror the exclamation mark (“!”) was not where it shows on the keyboard (again as per photo above); instead it was in ‘1+‘ key at the top left corner, only appearing after pressing “shift” plus “+”.

So now, since my software has been updated, the @ symbol - which is printed on the G key - no longer appears by pressing "right alt"+G (in fact what comes out is “ç” instead!), while I am still to figure out where to find all other symbols.

How can I fix my system, so that I can again have the Swiss German keyboard layout as per picture above, and generate symbols as shown on my keyboard, like “@“ by pressing G plus right Alt key?

Is there a software fix for this, please?...