Uno was working fine, now it no longer allows uploads

So, I have done my research and tried all of the solves, but I am stumped. Have an Uno (genuine) that I had been using for DCC++ with JMRI. Had been working flawlessly and then all of sudden it all stopped working. Board is correct. Arduino/Genuine Uno. I am using a Mac (Mojave) and the serial USB port is detected fine. However, when I go to the Serial Monitor set at 115200 baud, it no longer gives me the initial read out. This has led to the inability to upload anything onto the Uno. Can't even upload Blink. I have also tried the hold the reset button while uploading. Still get the same response of:

avrdude: stk500_getsync() attempt 10 of 10: not in sync: resp=0x00
Problem uploading to board. See Arduino Help Center for suggestions.

BN: Arduino/Genuino Uno
VID: 2341
PID: 0043
SN: 85731303533351117192

Try the Loop-back test.

If that works, check if you still have the bootloader running.

With the Uno powered on, hit the Reset Button and when you release it the L led should flash 3 times.

Did the problem begin when you updated to Mojave?

Ok, so I did the Loop back test and still wasn’t able to get the upload to work. I also tried the reset button and it did not flash 3 times. So, I’m guessing it’s a bootloader issue. What do I do now?

Mojave has been installed for some time and up until yesterday everything had been running fine with the Arduino Uno.

Here are screenshots.

You can burn bootloader with another Arduino using Arduino as ISP, and or a USBasp or Attinyisp.

I prefer a USBasp and think everyone should have at least two so the firmware can be upgraded easily.

I like the version with the 10pin to 6pin conversion as I have been able to program Pro Mini's and Attiny85 using the ISP pins on 8/10 pin packages.

I did the Loop back test

What was the result of the loopback test?

Here are screenshots.

It's much better to attach and embed pictures following these instructions

Just out of curiosity, I wanted to get a closer look at the first screenshot, but PhotoBucket wouldn't load it for me.