As one person mentioned already, you can paste images into the text editor on modern pages and we’ll upload the image for you.
Is this strictly asking for that capability in lists with multi line text box (MLTB)?
An error occurred while saving the commentJim Rood commented
Disappointed to discover that this functionality doesn't exist. Trying to create a reading list and wanted to have a thumbnail of the book cover display beside the title in the custom list.