Though the Highlander is pretty reliable vehicle, that is a LOT of miles for a ride share. IIRC some ride share companies require cars to be below a certain age and mileage - check before you shop.

https://www.carcomplaints.com/Toyota/Highlander/

https://repairpal.com/2010-toyota-highlander/problems

Here is a link from uber; you can enter car model and it'll tell you if you can use it or not. It also has a complete list of eligible vehicles. It's for Seattle based on my location but you can change it to where you live in order to make sure a car is eligible before purchasing it.

https://www.uber.com/global/en/eligible-vehicles/?city=seattle&uclick_id=9e10bd52-586d-4cf3-b72b-ec43718e22f6

https://help.lyft.com/hc/e/all/articles/115013077448-Vehicle-requirements

Also if doing ride share consider a Toyota hybrid; even a Corolla hybrid would do it.

You may want to double check what  @glen_stet said, I looked this up not too long ago and most rideshare companies want a car no older than ten years old.

I am not saying you chose a bad vehicle, they are very good for what they are. The ones you are looking at are high miles, I would be much more picky when buying one at that mileage. With that being said, I bought an 05 matrix with 191k, but it had good maintenance records, engine and trans fluid had been changed, and the car was taken care of.

At the very least, make sure the trans and engine fluids have been changed at regular intervals, trans changed at least once around 100k.

For rideshare purposes, the car is a gas guzzler. If you are doing city, or even mixed city, expect to get in the teens. If you are looking to make more on doing something like the uber luxury line, is it uber xl, or black, I would get something newer.

For rideshare, I would be considering something like a prius, or maybe rav4, or even rav4 hybrid, depending on your driving conditions you are expecting.