Checking for updates takes forever  

Hi, could you please be more specific.

Do you mean there's never an automatic check for updates?

Do you mean a manual check for updates fails? If so, screenshot please.

Please run the Windows update troubleshooter and post a screenshot of the result.
To post a screenshot please use the icon above your post: 'Insert image'

Despite the forum prompt when you wrote your post, I still don't see your Windows build number.

Have you ever done anything to disable Windows update?

Please post a screenshot of your Update History.

History: when did you first notice this?

Thank you for your reply.

Have you ever done anything to disable Windows update?
Please post a screenshot of your Update History.
History: when did you first notice this?

You did not answer these.


Why did I ask this? 'cos it's necessary to know the background before considering fixes.
Screenshots: remember I can't see your screen, and my crystal ball is currently down for scheduled maintenance.

Therefore, assuming you have never disabled Windows Updates by any means:
a. Download DNSjumper (free - just search) and check how long it takes your DNS to respond. (Click 'Fastest DNS' and check). State how long it takes for the fastest to respond.
b. Check your internet speed and report.
Search for 'Broadband speed checker' and use whatever's suitable for you in Spain.
c. Post a screenshot of your Update History (in Settings)

and then do this:
Reset Windows Update in Windows 10

Note: if you do NOT post a screenshot of your update history, this will erase it and it will be lost.

Then try Windows Update again, and report the result of that and of running the Windows Update Troubleshooter.

- coincidence and good luck, or something you fixed?