When linking to external websites from an app. Is it better to use web view or open in a browser?

In the example you shared of immigration to other countries, it should be clear to the user that this is outside your app. They should understand that they are getting redirected to an external source. Maybe even allow a choice so that they can choose to do it later. That will give them assurance that the information is accurate.

A slightly different point of view: give the user a choice.

Example that demonstrates why: The RSS reader Feedly on Android allows me to select the browser used (when I open a link or want to view the article I'm reading in a browser; it initially uses a slightly limited reader view for the latter). I choose Firefox over built-in, because I want a full-featured browser and to open in a new tab - I often do this when I have no signal. Others may choose differently as the internal view loads quicker assuming a good connection.

I don't know why I see so many old questions, but I'd like to answer this anyway.

Some questions you should ask yourself for each piece of content. If you answer at least one with yes, this strongly hints that you should use the browser instead of the webview.

Should users notice they leave the Apps context? Will users want to share this piece of information? Will they want to make a bookmark? Should users use links in that context? Will there be Links to some place outside your Website? Does the website provide some or all functions of the app? (There WILL be users that try to continue their workflow within this webview)

I could also put it another way: should the content actually be part of your app - then a webview makes sense. But then I ask you: why is this not part of your app?

The browser seems a far better option. Firstly, it signals to the user that this is something separate, since it's in their web browser. This also allows the user to, for example, Google a term they didn't understand within the browser, whereas if it were a web view they would have to switch apps. In this case, the browser is the best option.