Are there (developer) tools to remove files from Android "Rom" cache, if the smartphone doesn't start properly?

(I have also asked on stackoverflow, as I assume the use of developer tools is neccessary, but I would be very glad to get any working help on here also. The Google Photo App filled up the 16 GByte "Rom" of my Motorola G5: Google memory overview showed around 6.5 GByte of "Google Photo" data, whereas real (not deleted) photos and videos were only 4 GByte and I had moved those 4Gbyte to the SD card. To be on the save side before hitting "delete" of the 6.5 GByte, I removed the SD card beforehand. But now, when trying to restart, Android is stuck in the booting/start sequence. (I still can enter the pin, then the normal boot/start screen appears, but that only disappears shortly each 5 to 10 seconds. Stuck there.) **Question: Could I access in any way the "Rom" of the smartphone, so I could remove all or part of the 6.5 GByte occupied by "Google Photo", using for example adb?** I have Android 8.1 on the G5 and Win 10 on my computer.