I like your changes since I last played. The customizing and test area are great additions. The different arms for doing different things works well.
When I started the Master volume was at max, but the Music and SFX were at or near zero. I played a bit, then had to take a break. When I restarted later the volumes were back at the original settings.
The menu buttons could use with a hover effect/styling. In general, having a hover effect show what is and is not interactable helps a lot with UI.
The UI for customizing builds works, but could be improved. When I clicked on a slot it highlighted, but nothing else seemed to happen. I expected that it would pop up the options to customize it, or more details on the selected part. When I clicked on edit slots, it always selected the Base slot, regardless of which I had selected. If nothing happens, then you should probably disable selecting the slots above the "Edit Slots" button. When you click to edit the slots, I think it would be better if you always showed the larger view with the edit options. You could remove the Edit button, and move the Clear button down with Select. Cancel could also be removed, and End could probably go down there in place of Cancel. Clicking on the slot at the top could then update the lower section as if you had clicked on it and then clicked Edit. Right now it feels like too many clicks to do things, without a reason for the extra clicks. When I'm in Edit mode I expect that selecting the next slot will update the lower section, but I have to click on the Edit button as well. It works, but it just feels like there isn't a reason for the extra clicks. If you have more planned for in between, then this might make more sense. I added a new build taao experiment with, but wanted to remove it before starting the next step, but did not see a way to remove a build. I also did not see a way to rename them, which would be nice to have.
If you click on Edit, and then click End, without first clicking on Cancel, when you next click Edit Slots, the focus will be on the lower section and the Edit, Clear, and End buttons will not show. Clicking a slot at the top, even after clicking Cancel, does not bring them up. I had to Click Cancel, and then click on Edit Slots again, to get the buttons to show.
As I was writing notes from the base screen I noticed that in addition to pressing E you can also click to interact. It wasn't clicking on the console, but clicking anywhere, such as when I clicked to regain focus. Click to interact is nice, but it would be nicer if it was clicking on the object, when in range of course.
I started my first trip to the planet with just the default builds. I built 2 wardens, but mostly only used one. I built towers around the base and first crystals, and then set the worker to start mining. I explored and cleared the area with the warden, checking back to set the worker to the next crystal when they finished the one they had been on. Over time I built more workers and spread them out to cleared areas building towers nearby and then mining. I only built the houses after all the nests were cleared.
After building all the houses I clicked Return and created a custom build with a laser and construction arm, and using the Advance Base. I'm not sure what the Advance Base does, though I'm guessing more HP. I went back to the planet to try it out. The goal had not reset and still showed the houses I had built the last time as complete. I went ahead and played through since I was still only going to build them at the end. I completed that run with only the starting worker and my custom build. After I tested a new build with 2 mining arms to see if it would mine faster, and it looked like it did in the test area, as long as you clicked to use both arms. For my play style of building layered towers where I need defense, and exploring with a single warden, I think these 2 builds would be all I'd need. Perhaps as the game progresses and more difficult enemies show up, the extra firepower of 2 lasers, or newer more powerful options, would be needed. Right now I like having my exploration unit able to build towers, which can then be used to help fight off enemies if getting overwhelmed.
I found that the worker did not always mine the crystal I thought they should. I'd face a crystal and click on it, but they might start mining one off to the side. Similarly, I'd have them facing and close to one, but not be able to get them to start until I readjusted. The warden shooting the nests had a similar problem of it looking like the laser should be hitting, but no sign of damage. It could be rapid firing at the same spot, and suddenly it just stops showing any damage until I move the aim. I dealt with this by moving the mouse back and forth while shooting them.
Having played the older version, I went in knowing a bit of how things worked. Still, I think the UI does a good job of showing the hotkeys to do things. I think the core game loop works. It will need more, such as unlocking new parts, and new planets with different challenges, but it feels like you have a good core here. My kids watched me play and were comparing it to RTS games we've played.