I have had several varieties of blackberry and raspberry… and most will send up a single stemmed primocane… that will remain single stemmed and just keep getting taller…
But if you wait until it gets some specific height (say 4 ft) and cut off that tip…
It will then send out multiple forks in different directions frim that point where you cut it or just below.
The pic above is a herritage red raspberry… that i cut the tip off of as it got taller than my support rod.
See how it responded by sending out 4 forks.
That was late summer and on the tip of that tall fork to the right you can see a bumble on some raspberry blossoms there.
Bt Sept, Oct they look like this…
Most of the length of those forks will fruit in the fall.
The part that does fruit… will die.
In the spring i prune all the dead off… but leave the cane that is still alive… and the part that is still alive (normally the bottom 2/3) at each leaf node will send out fruiting latterals and produce a bunch of raspberries.
Below is a pic if what my spring crop looks like.
Those support rods that I use… I get at TSC store. They are 4 ft… made of fiberglass.
They are very durable and last for many years.
Anywhere a raspberry primocane pops up in my bed… i can just push one in and tie the cane to it.
I like them. From a distance you cant really see them. It just looks like your raspberries are standing up straight on their own.
A couple of purple royalty supported by the same rods. See how those purple royalty canes all forked just above my support rods… yep… l tipped them there.