What's the biggest difference between sales engineer and solutions engineer? Does one focus on simply deal making and negotiating while the latter is implementation? Are sales engr bonuses structured around how much they actually sell?

Nothing in my experience. Interchangeable titles depending on the organization. The trend in names changes every few years, depending on the company. Over the last 10+ years, I’ve been called sales and solutions engineer, product specialist, and solutions consultant. They’re all the same job with varying degrees of requirements depending on the stack you support. Pre-Internet bubble, we were often called systems engineers (at least in hardware). I’ve had a product evangelist role with a bonus structure. It was BS. Wouldn’t recommend an SE job with a bonus structure, at least in software. Software SEs are typically commission based performance, with a high base salary and an OTE (with a documented comp plan). The AE does the negotiations, legal, and pricing aspect of a sales cycle. I partner directly with my AEs to ensure a technical win, which can mean different things depending on the company. In my experience, gaining a technical win includes storytelling presentations & demos, proof of concepts, IT and InfoSec assessments / questionnaires, RFPs & RFIs, and lots of ad hoc questions along the way. Hope this helps!

Different company, but from talking to my peers- solutions architect (my role) is considered like a pre sales engineer and the titles are almost interchangeable. my AE does all the deals/money talk. My focus is implementations and new use cases/pocs . I do get commish/bonuses based on my regions performance.

Just a different name meaning the same thing. Some companies use certain terminology