Anyone here familiar with physical fibre types and could give me a bit of advice?

I am planning to put a network cable between my house and garage. The only feasible route seems to be the one the solar panel guys put their cables along: out the eaves of the house, down the wall, through a groove dremmelled between two paving stones in the path, and in through the garage wall. There's already an AC power cable on that route, so I'm looking at putting in fibre instead of copper as I won't be able to get any separation between the parallel AC and network cables.

I would expect to cable-clip it to the wall (I think flat plate ones with cable ties are recommended for fibre, yes? I think those have already been used for some of the other cables) and run it loose through the groove between the pavers - probably covered by gravel later. It looks like loose tube fibre is probably not right because the fibres would have a whole storey drop where they hang inside the tube and I understand that's not good. So probably tight buffered, right?

Do I need SWA or something, or is normal outdoor cable likely to be okay? Do I need to put it in a conduit to protect it from the elements? But if I do that, it'll be hanging loose inside a tube again and presumably that's not great.

Should I go for SMF? I would think if I install it right it should be fine and not need to go for MMF, but I'm not sure if there's any other reason to favour one over the other - it's only going to be 20m at most I would think. Do I need an attenuator for that kind of range?

Oof, I can't think what else I ought to consider. OM3 is presumably fine if going for multi-mode, and OS2 for single-mode. Are mode conditioning adaptors still a thing that are needed, for getting the right launch offset? I'm assuming not as I haven't seen any mention of them in my recent reading, but I just seem to have no idea…