I have a custom domain and configured the A-records properly.
The custom domain now brings me nicely to my retool installation.
The thing is that it ends up on the default login page of retool. Can I configure it in a way so that it always ends up on the default (Home) page of my app?
It sounds like you want to define your custom domain in such a way that it takes you to a specific app (yourdomain.com/app/yourapp/page1) instead of your org's home page (yourdomain.com). Is that right?
The short answer is that there isn't a way to do this without resorting to additional infrastructure. Are you running a self-hosted Retool instance?
Now that I think about it, there's a pretty clean way to do this if you are on a Business plan. It's possible to set a default landing page for specific user groups, as shown below.
The more intricate solution that I was originally thinking of wouldn't be quite the same. My idea was to map a DNS A record to a dedicated server whose primary purpose is to redirect the request to a specific Retool app.
Ideally it would go then to the default page of that app, with a custom login, but now it went again to the default login of retool. Can I configure this somewhere?
That's a good clarification - I wasn't understanding that you want to entirely bypass Retool's login page. In that case, you can actually replace the default login page with a custom app via the Branding settings.