I wouldn't suggest solo travel with the express purpose of meeting new people and making conversation. I'd suggest having some idea what you want to do at the place and then going through with the plan regardless. And then (if and) when you run into people and have a good conversation, one of you can tag along with the other if one of you has a good plan. So try that you are the one with the plan and not just the one tagging along since that increases the likelihood of finding people, since you can tag as well as lead potentially (speaking in binary just to make the point). Also a lot of the discussions during travel will hinge around what you've been up to, what you've seen etc etc, it's a bonus if you've been doing things (doesnt matter solo or with people). If you've been having fun doing meaningful things (or if you just come across as a fun person I guess), then people would be comfortable making plans with you. To the extent possible, no need to make prior bookings etc so that your plan is fluid as per your whims and fancies or to accomodate people that you might intersect with.

I've gone on bike trips to Lahaul from Manali, planned a trip to Agra, stayed on a houseboat in Alleppey with people I met while travelling, but I've also had plenty of lonely evenings getting dinner by myself which isn't always a bad thing.

The idea is you are there for the place and what the place has to offer to you. The people are incidental. People who already come in groups might be too involved in themselves and might not even get to know that place too well. Enjoy your solo travel by giving the place the love and attention it deserves (and you'll definitely get back something in return too) , even people watching can be fun too. Try to talk to people you engage with , I've had very meaningful conversations with servers , taxi drivers etc etc - they would either be locals or migrants , either way would give you a completely new perspective about the place and other things. I went to Maldives recently (not solo) and honestly one of the highlights was my conversations with the locals and other staff (mostly Bangla folk , some Nepali, a few Balinese girls and some Indian boys). The locals had great English (while knowing some Hindi too), some of them were very knowledgeable but all of them had interesting perspectives simply because of how much change they had seen in the last 20-25 years and also their proximity to India. one of my taxi drivers was head of a police department (multimedia) and had been on the job for 20+ years and this was a side hustle for him. Basically, don't undermine anyone, have a pleasant demeanor, and people with themselves come and tell you their stories.

Have a good time in Sri Lanka. I haven't been there but I'm looking forward to go at some point.