I would like to know if it is possible to customize the appearance of the nextion upload screen.
The screen I refer to is in the attached image.
Hi and welcome @Dener0987!
No, currently there‘s no option to make changes to the bootloader messages or their appearance. Nextion won‘t make it modifiable for sure since it would require drastic changes in their firmware.
Maybe someone will find a way to fix ar least the spelling errors or change the font, but that‘s about all you can expect and even these small changes won‘t happen anytime soon.