As a heavy rider (~135kg 300lbs), I got a Diamondback Overdrive 29" bike to help me lose weight. After riding a few times with my family, my rear wheel keeps deflating/bursting. I have read previous posts on here and inflated the rear wheel more than was set up yet the issue still remains. Upon checking the bike specs, it states that the max weight is 100kg 😔. Can I continue to use this bike but change my set up (different tunes, pressure..) or do I need to buy 'another' bike? Please help as it's frustrating to get 3/4 through a ride before getting a flat.
Manufacturer weight limits on bikes are a little nebulous in that they're not totally meaningless but they tend towards estimation, liability protection, and a fair line for the warranty department to take when a bike eventually breaks under a heavier load then they designed for. Going above it is an at your own risk thing because forks, wheels, and frames failing are all real and dangerous things that are only going to be at greater risk of happening as a result. In practical terms though, those kinds of worst case scenarios don't happen very much as a result of exceeding weight limits on non-exotic mountain bikes by this much.
What is at pretty good likelihood of happening is the wheels not really holding up over time. The usual case is for heavier MTB riders that ride a lot to burn through the stock wheels pretty quickly and then get something with a heavier weight rim, ideally handbuilt and with 36 spokes. If you want to, it could be reasonable to skip the step of tacoing the rims that came on it or dealing with them going out of true repeatedly and just upgrade now.
As for the flats, you don't say what's causing them, which suggests some odds that it's one of the common causes of repeat flats and not related to weight. The really common ones are a rim strip that's not doing its job, something lodged in the tire, or tires/tubes that aren't puncture resistant enough for where you're riding.
If you're pinch flatting, the main remedy is more pressure, and failing that more width.