There is no universal number, but there are two boundaries and the answer lies between them. Below is regularity; above is the reader's patience.
The lower boundary
A channel publishing once a fortnight is forgotten. Not because the posts are poor — the reader simply does not remember where it came from. One post a week is usually the minimum for staying in view.
The upper boundary
Five posts a day is sustainable only for news channels, and not all of them. A normal topical channel at that volume loses subscribers faster than it gains them: notifications start to grate, the channel is muted, then dropped.
This is most visible when cloning several sources — how many channels to clone.
Finding your own
Change the frequency once a month and watch two numbers together: average reach per post and unsubscribes. More posts almost always lowers average reach — that is normal. What is not normal is unsubscribes rising with it.
What matters more than frequency
Evenness. Three posts a week every week beats ten one week and none the next. An audience learns a rhythm, and a broken rhythm is noticed sooner than a change in content.
And about quality
Raising frequency only makes sense when there is genuinely more material. Padding for the sake of a schedule is spotted instantly — the robot feed.
How Neurogram does this
Everything above is manual work that runs into the number of hours in a day. Neurogram does it on your own accounts and without you: it collects channels and audiences, writes comments and replies with a language model, and keeps limits and quiet hours so the accounts survive. See pricing or look at your case.