I currently have no screen for my PC. So I wanted to ask if I could also use my laptop as a screen for my PC
There are very few laptops where you can use the HDMI port as an input, so it will most likely not work for you.
But you can e.g. Use a television. You only have to see if it has a graphics port that your PC also has.
Very unlikely that this is possible. Notebooks have HDMI outputs, but hardly any HDMI inputs. I don't know anyone who has that.
A laptop is not actually intended for this. But there's a (not serious) solution: unscrew the laptop, take out the screen with the cable, there are adapters to HDMI, the laptop is unusable afterwards
As the others said, you can't really do that. But if you don't care what type of screen you have, you can get an old monitor for 15-25 euro from Ebay classifieds. Many still have to mess around.
Today's flat screens also exist as TV telly. Newer models have VGA or HDMI or both as a connection. There are hardly any tubes or CRT monitors left. Such a TV can then also be used as a replacement for the monitor for the PC
