It is good to concentrate on work, enter the zone, and contribute with joy.
It is good to enhance the zone, become accustomed to the zone, and work with the zone every day.
It is good to live with a constant joy that emerges as if replacing the zone.

This has been called Samadhi with an object (Samprajnata Samadhi) since ancient times.

When the zone becomes stable, concentration will reach its peak, and eventually, you will begin to relax in a state of emptiness.
In a state of emptiness, you will be able to recognize objects as they are.

As the state of bliss becomes stable and relaxation deepens, Kundalini may awaken and be filled with energy.
When Kundalini stabilizes and rises to the abdomen (Manipura), chest (Anahata), and head (Ajna), a state of stillness will appear. This is a state of observation, and it is also what has been called Vipassana or Samadhi without an object (Asamprajnata Samadhi) since ancient times.

Eventually, the state of stillness will become stable.
And suddenly, you will begin to feel the presence of your higher self or Atman, which you were supposed to have been with all along, and eventually, you will merge with the consciousness of that higher self (or Atman).

Once, Kundalini has reached the Ajna chakra, but the next change is in the chest (Anahata), so it seems like you are temporarily returning to a previous stage, but in reality, connecting with the consciousness of the higher self is a great leap.

By merging with the higher self in the chest (Anahata chakra), you will feel a deeper sense of bliss, and you will intuitively realize that there is an eternal being, and feelings of gratitude will well up, naturally filling yourself, and words of joy such as "thank you, thank you" will naturally come from your heart and mouth.

This point can be considered a certain spiritual milestone (the first), and it seems that merging with the higher self at this stage is truly the beginning of spirituality.

Initially, the fusion with the higher self will occur through the heart (Anahata chakra).
After that, the consciousness of the higher self will rise again, reaching the throat (Vishuddha) and then the Ajna chakra.

Supplement:

This final state can be called Samadhi, but it is a state that is not even appropriate to call Samadhi, because it is not an action or a state, but existence itself. Simply calling it the consciousness of the higher self or Atman is just right. If you were to call it Samadhi, it would be appropriate to call it Sahaja Nirvikalpa Samadhi, as said by Ramana Maharshi, but even that seems unnecessary. The fusion with the higher self occurs gradually (although relatively quickly), so it is not yet strongly fused to the point where it can be called "Sahaja" (natural), nor is it appropriate to call it "Kevala" (temporary). At this stage, the consciousness of the higher self merges with your ego consciousness, and consciousness expands. Then, things like Samadhi become irrelevant. There is only expanding consciousness, and that is all. It is a matter of what to call it, but simply calling it the higher self or Atman is sufficient. By reaching the consciousness of the higher self, there is a feeling of transcending Samadhi or completing Samadhi. Some schools of thought link Samadhi with supernatural phenomena, but if that is the case, it is better not to call it Samadhi to avoid misunderstandings.

Ajna is supposed to be the gateway to the next stage, but I am still at Vishuddha in my throat, so for me, further progress will be a pleasure for the future.

Whether Samadhi has an object or not corresponds to whether it is in the material realm or not. Up to the causal (Karana) level, it is material, so Samadhi before the Higher Self is a Samadhi with an object (Samprajnata Samadhi). However, even before the Higher Self clearly manifests, it temporarily becomes a state without an object and partially connects to the Higher Self, which is why it reaches a state of stillness. Simply concentrating between the eyebrows and temporarily reaching a state of stillness does not yet mean that you are firmly connected to the Higher Self, but it is a state of temporarily connecting to it, and therefore, in a state of stillness, it becomes a Samadhi without an object (Asamprajnata Samadhi). On the other hand, after connecting with the Higher Self, a Samadhi without an object (Asamprajnata Samadhi) becomes the basic state. In that case, Samadhi is no longer even an "action," and it becomes a natural state, to the point that it feels strange to even call it Samadhi.