When developing on Yii2 (and not only), how to deliver updates to customers of your system?

Question

Yii

For example, we developed a service on Yii2, other customers will buy it, you need to somehow deliver system updates to their servers. System one can say CMS.
How can such a solution be implemented?
The first problem, for example, is templates (each customer has his own, we use the templates folder built into Yii2), you need to somehow deliver certain templates to certain customers.
It would also not be bad to deliver the general code in parts or all for a start.
There was an idea to make a GIT repository on the server (a \ kov) and a remote repository for each client, and thus push the code to them. But you still need to run migrations and keep track of whether nothing has fallen.
In general, there is no particular experience in delivering updates, it is interesting how knowledgeable people do and what they use. And in general, what options are there, except for uploading files manually.

Answer 1

I have made a step-by-step update process:
1. On my site there is an archive with the update (the whole folder along with the vendor)
2. The system administrator downloads the archive and uploads it to the system (this can be automated)
3. The archive is unpacked and migrations are applied (in transactions)
4 All project files are being replaced
Ideally, make the update system independent of yii2, so that when the whole system crashes, it will be possible to roll the update with the fix