I've tried to make this foolproof and while the likelihood of unrecoverable things going wrong is extremely low, it's never zero. So proceed with care.
Once you start Write flash from file or Flash CrossPoint PaperS3 firmware, you should avoid disconnecting your device or closing the tab until the operation is complete.
If your device is not detected, you may need to enter download mode manually: hold the BOOT button (G0) while pressing the RST button, then release both.
Full flash controls
These actions allow you to read or write the entire 16 MB flash of your M5Stack Paper S3.
Save full flash will read your device's flash and save it as flash.bin. This will take around 25 minutes. You can use that file with Write full flash from file to restore your device later.
Note: The M5Stack Paper S3 does not ship with downloadable factory firmware. If you want to preserve your stock firmware, use Save full flash to create a backup before flashing CrossPoint PaperS3. There is no other way to restore the original M5Stack firmware.
OTA fast flash controls
Before using this, I'd strongly recommend taking a backup of your device using Save full flash above.
Flash CrossPoint PaperS3 firmware will download the latest CrossPoint firmware for M5Stack Paper S3, overwrite the backup partition with the new firmware, and swap over to using this partition (leaving your existing firmware as the new backup). This is significantly faster than a full flash write and will retain all your settings. If it goes wrong, it should be fine to run again.