Bolt mystery

[Goran]

Hello, I hope you are all keeping well during this crazy time.
I have been away for a while, life got in the way, but I'm still driving the old D2.

I was doing an oil change today, and discovered this large bolt on my undertray. A bit worrying!

The main work I had done recently, and by recently I mean around 5 months ago, was a steering rack change after the old one leaked out all the steering fluid.

I managed to get under the car, but as far as I can see the steering rack bolts look different to this one.

I did notice that one location on the gearbox seems to be missing a bolt. I checked inside and there is definitely thread on the engine block side of this hole.

Could I be missing a gearbox-to-engine bolt?
Oh I forgot to say, its a manual gearbox, so the bolt pattern is probably different to the auto box.
The parts diagram does seem to show a bolt in this location, but its a different type of bolt than the one I found.
The photo is from the left side of the gearbox looking forward.

Would someone changing a steering rack need to remove the gearbox?

Thanks for your help.