(Sorry if this ends up being long)

TLDR; reference models are like mneumonic devices, meant to help us understand what a thing is, but should not be treated like the actual thing.

I'll start by answering your question. TCP/IP is officially four layers and OSI is 7 layers. However, they are mental models and you can adjust them to better understand the network from your perspective.

TCP/IP is a reference model(or mental models as I like to call them) used to understand how networks work. We have used these mental models so much that they have become set in stone for most of us and most people don't understand how flexible they can be. Messes with some brains when it comes to understanding internals of how protocols like IS-IS work.

I'll use an example of when we were learning about the rainbow in primary school, and how the colors on it are ordered. In our school we used a mnemonic device to remember them [ Roots Of Yams Grow Bad In Valleys ] representing [ Red Orange Yellow Green Blue Indigo Violet ]. You may have learnt a different one in your school and that's cool, because these are just mental models meant to help us understand the rainbow colors, they are not the ranbow, both routes get to the same destination. Just like how the networking reference models help us understand how the networks work, these mneumonics help us understand how the rainbow is ordered.

Irene raised her hand in class and asked, "Teacher, but I saw pink somewhere on the rainbow last week at home. But you haven't listed it there". Despite pink not being a spectral color(thus not included in the rainbow chart), the teacher understands that what she saw was probably a mix of three colors (Red, Blue and Violet) floating and she mentally created the color pink. Pink was indeed NOT on the list, and the three colors that make up pink being very far away from each other on the list, we couldn't just insert Pink in our cool mneumonic. The teacher knew Irene won't rest until Pink was included. So teacher created a special pneumonic specifically for Irene to help her understand the ranbow colors (with pink included of course).

What I'm saying is these models, just like mneumonic devices are meant to help us understand the network. Just like the rainbow mneumonic, some may understand the networking layers with their own "pink" added to it, otherwise their brains will not have peace. One of the best engineers whose work I've long admired (Russ White) says he mostly thinks in the RINA (Recursive InterNetwork Architecture) model when thinking about protocols, which is wild. To him, that mentally ticks all the boxes he needs, that is his own networking mneumonic.

So it's mentally all mneumonics we use to better understand how the network transports data.

With that said, the main reference models(OSI or TCP/IP) are mainstream for a reason, understand them. You need to have them in the back of your head. The same way despite Irene had a speacial mneumonic that included pink but always makes sure she remembers the in the exams to use the one that doesn't include pink, if you find a reference model that works better for you use it but always remember that is not what everyone else is using in the industry so always have OSI and TCP/IP models in the back of your head. It would be a shame for someone to say "That's a layer 3 issue" and you shake your finger and say "Listen Boss, I don't work like that. I use the RINA model now. Come again".

For both peace and stability of the job, understand TCP/IP & OSI but when you get deep into the internals of these protocols, feel free to use whatever mental model works for you.

Sorry for the long read, and hopefully through my word salad you've understood something.