There are two ways to resize the Bootcamp partition: delete Windows from the Mac and recreate the Windows partition(lose all data on the Windows partition), or shrink the space of the Macintosh HD partition and merge the untitled space to Bootcamp with third-party software(no data lost).
You have already tried some Terminal commands to write in MBR, run First Aid on the Bootcamp partition, and use a third-party repair tool, but all of them fail to fix the Bootcamp partition loss issue. According to the screenshot, the Apple Boot partition (620MB) is missing, you have deleted your local recovery partition, so you will need to fix it with these steps:
- Create a bootable install for macOS and boot your Mac from it.
- Then, enter macOS Recovery Mode to disable SIP.
- Upgrade macOS to match the version on your internal disk.
- Delete extra partitions on the 2012 MacBook Air.