Nevertheless I think it is reacting to the setting being too dark for it - the jade behind certainly has the type of leaves these often produce under ordinary indoor conditions, where the light levels are not high enough for them to have what could be called "sun foliage".

It looks healthy, but slightly etiolate. That’s why it’s looking the way it is, some cactus are “crawlers”, they grow more on the ground like a snake. Yours doesn’t look like it naturally does that with enough light. I think this because the growth is getting skinny towards the top. Also, If I had to guess your cactus is some type of Echinopsis, which aren’t “crawlers”. Your cactus doesn’t look too bad imo. The only thing to fix this is more light, the new growth will be more robust, but the old will not revert.

The funny little strings coming out are roots. You can leave them or cut them.

The new growth is a good.

Lastly, the scabby marks are nothing to worry about the cactus once had some type of damage, and now has healed itself🙂.

Thank you Embothrium and Kara for your thoughts. I will try and improve its light conditions and give it more sun. So would you not advise trying to report it in a more upright position? It’s so drastically different to when I got it I.e. completely vertical. it’s a bit awkward to place like it is but it doesn’t bother me as long it will remain healthy In that position. I’m a bit worried about the stress it must have with all the weight on that bend being so unbalanced.

Another question is about the proportions of the pot to the plant? do they seem ok, I’ve read the shallower pot the better to avoid excess water remaining in the soil But maybe the ratio is good for a cactus of this size? This is how I bought it.

I’d like to put it in more attractive ceramic pot anyway, would you put it in as it is or would you get rid of the plastic ?

Actually the shallower the pot the more of the total volume of potting medium the perched water table that all containers produce occupies. So to give a plant a larger space above the perched water it is moved into a taller pot.

The perched water table occurs because water draining through soil inside a container backs up when the bottom of the container is encountered, until the involved zone of the medium becomes saturated - at which point the water then drains out. This happens every time a plant is watered, resulting in sufficiently drainage sensitive kinds of plants not rooting much, if at all into this lower, repeatedly saturated level. Which in a squat container may consist of nearly half of the total volume of soil.