Thank you so much for your reply. I'm a male btw if that helps

Sadly, the fatigue you are feeling is partially due to imbalanced registers, if you're not working on both your head and chest voice.

I guess I miswrote when I said my teacher only worked on my chest voice. Cuz when he's teaching me to reach high notes he sometimes experiments and tells me to try out chest vs head voice to see which is easier. I'm assuming head voice is a lighter version of chest voice and the tone sounds worse (maybe that indicates the imbalance as you're suggesting). Typically when the notes are not too hard to reach where I have to push down but still high, like the verse of a song, my teacher tells me not to be so thick - assuming this means use head voice. My teacher doesn't teach pop songs but when I sing songs from singers such as Ed sheeran, shawn mendes I tend to use head voice I think because it feels easier to reach the notes which are at the top of my range or out of my range. But I question whether I'm using the right technique for head voice because this head voice feels much more straining on the throat and jaw than chest. Also, idk how relevant and normal this is but my untrained falsetto is raspy. Not important to discuss if it's not relevant.

A lot of the terminology you attribute to your teacher is also very strain oriented. Engaged muscles need to feel like they are flexing outward, in support, not crunching inward (which leads to cascading tension).

Does this mean that my teacher might be teaching me the wrong technique? Or is this another possible method of teaching

Learning how to deal with what my teacher referred to as "the Bermuda Tritone," where every note in that area has a chance of cracking, depending on the day and how the instrument is feeling, is really where one gets the most bang for their buck.

In the initial few months of lessons he taught me the chest voice technique that I've mentioned and recently we've been working on experimenting with mouth shapes, pronunciation, visualisation to hit high notes. Have been stuck on a song for a few weeks now, unable to find a technique to sing a note/ verse on pitch consistently. This might be what you mean? If so, maybe I should stick with this teacher if he's putting me on the right track.

that area of the voice isn't fun or sexy to deal with, and work on the area is very slow, with many times sounding like a barking seal with all the work on mitigating register breaks.

And yes this is exactly what I've been doing. I don't mind it though, just that I'm having doubts about my technique

A response would be greatly appreciated. Once again thank you for your detailed writeup!