@fikirsancisi61 when the ubuntu recovery starts did it show slot a or slot b? I had success only on slot a. Also make sure you have stock android 9. You may have to do a fastboot flash of the files.

@fikirsancisi61 I have moved your post to the device sub forum. Have a look through the other posts there might be an answer there.

Another thing I have discovered is the USB port isn't too accommodating with certain USB cables. To solve this, I fold a piece of paper and when inserting the cable, put it on the bottom of the cable connector as I insert it. This holds the cable in tight (all the USB contacts are on the top of the connector) and the phone won't lose communication with the PC if you move it, nudge the cable, breath etc.