This question brings a lot of nostalgia :)
When we were exploring a possible Q2A platform for our site (GATE Overflow) in 2014, we had the same concern. Q2A in fact hasn't changed much since then - major developments happened before 2014 by Gideon and IIRC we started with version 1.5.3 and now it is 1.8.8 which we are now using on Ubuntu 22.04 and PHP 8.3. There have been no issues for Q2A support - thanks to the contributions from Scott, Pupi and Gideon.
We are also extremely thankful to @gold-developer for the wonderful themes - which is a major improvement for us over the last few years. Being a feature-rich website, we cannot use just any theme and here is where themes like Polaris, Muffin etc. are irreplaceable.
Over our near 10 years experience, I think we made a great decision using Q2A. The fact that Q2A is built on native PHP and MySQL means, it is straightforward to extend features - we have made a number of plugins, many of which are open source, without spending months figuring out how to do them. Some of the Q2A users like Noah and others have also shared many useful plugins which are working even after 10 years since the last commit :)
Since there are many users from India here and our website is also from India, let me add a few points regarding how our website is run. Initially, we were relying on google ads for our revenue, which was okay. But being an educational website each ad click used to pay < 0.08$ which was enough to pay for the server expenses but not for the editors (yes, we have editors on our site to add previous year exam questions in an organized way). Also, once google removed the 4 ad per page policy the ads became a nuisance - especially for an educational site like ours and we had to get rid of them. Fortunately we could add an exam system in our Q2A - exams are added similar to questions and we had to just add an interface to take exams. And paid exams is what helps run our website now. So, if you are in India or similar developing country and think google ads can help run a Q2A website - better not try for it.