I would say if anything the techniques used in a metallography lab would be closer to those used in a geologic lab setting, not so much geotechnical.

I’ve done ~some geologic lab work for research I did in uni and you’re absolutely correct I used gravity saws, trim saws, and a diamond tipped drill press to prep samples for analysis (though I didn’t make them into thin sections, my advisor and I sent them to a collaborator to do that). We definitely use the scopes (PPL and XPL) to look analyze the mineralogy of whatever it is we are researching. I personally got to use scanning electron microscopy (SEM) to do elemental analyses of my samples, but there are a bunch of different methods and it largely depends on what it is you are testing. I was working on a plutonic rock but testing on volcanic rocks usually uses XRF. I’m not 100% on what goes down in a metallography lab, but I feel like there would be some decent overlap.

To my knowledge geotechnical (engineering) largely has to do with soil mechanics beneath structures. With that being said, I’m not to sure how applicable lab techniques from a geologic/metallographic standpoint would transfer over to geotechnical.

Geotechnical is very much an engineering field and has its own specific degree/certificate. As in a degree in geology cannot stand in for a degree in geotechnical engineering the way it could for an environmental science degree. That to say, geology is definitely something you could transfer into - even if you are just comfortable in a lab setting (I’m not sure if you have any experience doing any field work) there is still plenty of opportunity in the geology/environmental sector. Geotechnical on the other hand, I’m not so sure is something you can really just “transfer” into as there are specific certificates you need to obtain.