Facebook and YouTube pages can't be opened, but do they work with an active VPN?

If I want to access facebook or youtube on my computer (at home, connected to Fritz! Box), nothing is shown to me.

In Firefox I only get a white page on both calls. In Chrome I get the message ERR_CONNECTION_RESET on Facebook. YouTube can be called up, I also get the preview of a video when I point it with the cursor, but when I open the video, I see the familiar surface but in the video window only the loading circle rotates and nothing happens.

I have already reset my WLAN, made DNS flush, switched firewall off and on again, uninstalled and reinstalled browser, deleted browser caches, tried with a private window… It just doesn't help.

The strange thing: When I open a connection to a VPN server with OpenVPN, the two sides work again as normal.

I did not install any new programs and did not carry out any updates before the problem.

After updates (tools + hardware) I have been looking for the problem and have also installed pre-existing ones. But that doesn't help either.

At home I have a Fritz! Box 7590 and in another room a Fritz! Box 7362 SL (this runs as a mesh repeater).

I have already connected my notebook to the 2.4 and also to the 5 GHz Wi-Fi from the 7590 and also to the 2.4 GHz Wi-Fi from the 7362 SL.

Facebook and YouTube always behave equally badly.

Does somebody still have an idea? Because I don't want to set up the whole part from scratch.

Another important information would be:
If you go to the side with another device (e.g. Cell phone), does it work properly?

ERR_CONNECTION_RESET means that there's no DNS problem.

If no filters are set in the FritzBox then it may still be that you have landed with your IP on a blacklist and that you are blocked by some pages. A tracert can help narrow down the problem.

Have you ever tried to get a new IP by restarting the Fritzbox?

Oh yes… So with another notebook and 2 cell phones the two sides work in the same network.

I forgot to mention that it works perfectly on the same network with other devices (another notebook, other desktop computers, 2 cell phones and tablets).

Oh so ok that changes a lot of course. Which firewall or which virus software do you use?

I only use the standard Windows stuff.

Should I guess?

No, I have no additional software installed. I use what is already included with Windows 10.