This was the start of a track by a canal in France that got muddier and muddier.
It was more like clay and eventually clogged my v-brakes and derailleurs up so much that I couldn’t even push my bike without digging it out with my fingers. I don’t have fenders, but I can’t see how they would have helped.

My companion on the other hand has disc brakes and fenders. He kept on riding.

When we eventually made it back to a more hard packed surface, we luckily found a canoe club that had an outdoor water hose 😅

it was the disk brakes instead of v-brake calipers. fenders no help!

^^^ that‘s exactly what it looked liked

I released the J-pipes on the brakes to get as much clearance as possible… all to no avail

Sometimes mud isn't so glorious. I had one instance of mud that did me in. Described in more detail on a blog post - Fairbanks, long day - A bicycle ride across the Americas but the thumbnail summary:
- On the Dalton Highway southbound near mile 90 the road became gravel. It was also raining.
- Texture of the mud changed, initially it was more of a softer "peanut butter" texture. Soft, gooey and slippery but I was still able to navigate with some caution to avoid slipping on downhills.
- The texture slowly changed to more "adhesive paste" that completely adhered to everything.
- At mile 75 the adhesive paste jammed my chain and before I knew it I torqued off my derailleur. I wasn't the only cyclist affected, two Swedish cyclists with Rohloff hubs had the paste get in and jamb up the hubs.
- I walked 7 miles before a kind couple stopped and gave me a ride to the Yukon River Camp another 14 miles further. Here I stashed my bike behind the camp and hitched a further ride from there in a tourist van going to the Arctic Circle and back. This got me back to Fairbanks.
- The next morning, I rented a vehicle in Fairbanks and drove back up and retrieved my bike. Brought it to a bike shop for repair before I could continue my tour.

I was a spectator at a cyclocross race about a decade ago. Snapped this photo.

funnily enough, the only time I have had to stop and dig out mud accumulation was here in Montreal, on a dirt gravel path that I have taken hundreds of times.
Now it was a long time ago, and I guess it was just bad timing of when I rode, or they've redone the surface since then.

I guess it comes down to how dirt is, if its more clay-y , or if there is more rocks and pebbles in it, and I guess also how much rain there has been over a given amount of time and how much things can dry out.
Other times I've ridden in lots of rainy conditions on dirt and luckily (so far) never run into it as badly to cause build-up.

drivetrain and rim brake killer though.....

This is ok.... any problem there.

This is mud!