1. I will not prefer using this technique.
2. If you will create landing page for different countries like, xyz.com/de & xyc.com/uk . Then, you will be having issue with creating landing pages within these URL's and also It will not well optimized for SEO.
3. This is the best practice, because you will have more domains, more DA, and you can get link from your each domain. Also, you can optimize every single domain locally. It will rank faster and boost your local search within the country. Get hosting within that country from which the domain belongs to.
I am using same technique for my website with multiple languages and hosted with Cloudways SEO hosting, you can them, https://www.cloudways.com/en/seo-friendly-hosting.php. They will give you datacenters within your target country. and precisely it will be optimized.
It really depends on your app. There are "data safe harbor" provisions in places like the EU that preclude you from physically holding certain types of data about EU citizens in a location outside the EU borders.
There are datasets in the USA that the US government requires you not hold outside the USA.
And there may also be authentication and Content Delivery (CDN) reasons to have local front end presence.
So there Is simply no single answer for this