Probably not unless the reply to this issue from 2018 https://github.com/flameshot-org/flameshot/issues/381 is hinting about a rc file instead of recompiling with the button disabled in qmake.

Edit: I went on reading the code. The image uploader is hardcoded into https://github.com/flameshot-org/flameshot/blob/97c195452293... and I didn't find anything to conditionally remove it from the UI. But I won't bet a coffee on it after only a 10 minute cursory scan of the code.

In the config, there is a checkbox for the image uploader https://i.imgur.com/pTiY2ul.png

Use this config option: https://ibb.co/XS6TsXS

I just had to execute 'flameshot config' and to disable the Image Uploader button.