What would be the correct way to build an application?

Question

Flask

Hello, I am a beginner programmer, so far I have only studied the "naked" languages ​​python and javascript, well, I know the basics of html and css. I also tweaked react a little.
Now I began to study flask and I'm trying to write a simple application: the client web face in the browser displays data from the database (sqlite3), and then you can add some forms to write to the database.
And a question arose. As I understand it, you can do this in the following ways:
1) Pages are formed on the server side, using a template engine, and ready-made html is sent to the browser.
2) The server part packs the data in json and, upon request, returns not html but json. The client part already builds an interface with the data from this jsona. Then, to build the client side, you can use some kind of javascript framework, such as reacta or vue. But is it necessary? Of the advantages of this method, I see only the ability to make SPA, that is, the work of the client without reloading the page.
I would like to ask professional developers what to do when building such applications?

Answer 1

the second one is still worse for SEO
, I think, 3-5 years will be equal or even the second one will be preferable
+ there are a lot of tasks where SEO is not needed - for example, access from Mobile to a directory / corporate site