I only have 5 plugins.
But then I’m not technical and my site is basic

As many as it takes to create the website that you want to share your message.

The caveat is that every plugin can have an effect on your website some positive and some negative.

Speed being top of the negative impacts.

When adding plugins, it can pay to do a speed test before and after.

Then evaluate whether the functionality gain can be balanced against the loss of speed or not.

Also before adding, ask the question why am I adding this plugin, what am I hoping to achieve.

Everyone seems to have a different opinion about this, but the less the better. WA recommend you only use 5 or so, but that's really hard to achieve.
What you want to check is how well the plugin is created. I understand that some plugins will slow your website down if they are not coded well. If you can, look up reviews on a plugin that you want to install. This may give you some idea if the plugin is created well.
I've just installed my 20th plugin but I've heard of other members having many more.

It is suggested in the training to only use 5 however often we use more depending on our needs when building.
The biggest issue with too many is slow site speed and you don't want this as your traffic will stop as people hate slow sites
I hope this helps
Vicki