QR codes show up in slides, WhatsApp forwards, and PDF posters. Pointing your phone at a monitor works until the room is bright or you only have a laptop. A screenshot plus a browser scanner is usually faster.
On QR Code Scanner you either allow the camera or upload the image. Decoding stays on your machine. You get the raw text or URL in a box. Copy it. Check it. Then decide whether to open it.
Why the page does not open the link
Anyone can put a nasty URL in a QR code. Showing the string first is slower and safer. If it looks like your bank but the host name is wrong, you already know not to tap it.
If the scan fails
Crop tighter. The code should fill most of the frame. Avoid a photo of a photo of a photo. Low contrast (grey on grey, or a code printed on a busy background) fails more often than a slightly small code on a white page.
Product barcodes on tins are a different shape. Those go on Barcode Scanner. To make a code rather than read one, use QR Code Generator.