For uploading instagram posts the images need to be on my phone, so I tried sending the image on WhatsApp Desktop so I have it on my phone but this doesn't save it in the gallery. What can I do, to automatically store these images and videos in my gallery. If this is not possible, is there an app...

I have a galaxy S20+ and a generic USB c to HDMI cable. I connected the phone to a Philips monitor but I don't see anything on the monitor and in the USB settings I only see USB controlled by: connected device. And when trying to switch it to This device, I get an error saying "couldn't switch". ...