The compass works disgustingly!

This won't be of help, but I just checked the compass on mine and it's working well.  I'm current on all updates, 26.18, maps, etc...  You might try a full reset and see if that helps.  Of course it helps to keep it well clear of anything magnetic that could affect its reading.

I also have this problem where when I come to a stop, the map immediately reorients, usually 180 degrees, but then resumes expected function when moving. It's been like this for a few months at least but maybe I didn't notice prior.

Ahh.  I might not be seeing that problem because I have my map orientation set to North always up.  I only use the compass separately from the map. In previous Edge units that didn't have magnetic compasses, they only knew direction by which way your GPS position changed while moving.  While stationary, they couldn't tell direction, or would swing around based on GPS position noise. 

When the 1040 was first released Garmin made a statement saying that the Compass was calibrated during assembly and would "never" need re-calibration. Of course users quickly found that this was not true and garmin admitted there was a compass calibration in the hidden debugging menu. To stop users bugging support with this bug an early software release exposed the hidden function, I have to do this every few weeks, it generally works once you get the hang of the process although people will think you are playing aeroplanes with your Garmin, give it a try.

(Menu > System > Calibrate Compass)

https://www8.garmin.com/manuals/webhelp/GUID-16B12CFE-F96E-4DE9-9F5F-8C4A5936D3B9/EN-US/GUID-71115C13-A2F3-4A34-984F-F5A864476677.html 

Thank you! But I always see the “calibration complete” message as soon as I start it. Right now, I don't have the ability to go out into the open with the device. I'll try calibrating the compass again. Perhaps I wasn't doing it slowly rotate enough.

The compass works ok but no longer links to the navigation - only display the direction, before the arrow was showing the final destination point which was much better and more useful.  Now I found the feature useless (and not to mention the new design which is not as good as before). WHY BREAK SOMETHING THAT WAS WORKING PERFECTLY???!!!!!

Same, but my EDGE 830 does it also. If I mount it close to my stem (metal) it has a 20º bias. Take it off and hold it in my hand, and it's accurate. Same with my EDGE 840. There is virtually no steal in that area, and aluminium should't interfere. Maybe the steel fasteners of the stem and handlebar? 

It's a little better on my gravel bike with an out-front mount. 

FWIW, I just checked my Edge 840 compass. It has never been calibrated but it works just fine when stationary. If I stand in one place and rotate my direction, the compass changes accordingly. 

I'm also on 26.18.

If the calibration process does not work then there might be a fault with your hardware, call Garmin support in your region and if they can not make it work get them to replace it.