Riding a bike can be so fun and freeing even at a hefty weight, it kind of brings you back to your childhood.
I do have some advice, but I will give the caveat that my experience was around the 300lb+ range, but a lot of it probably still applies.
As you said, of course avoid any big box store, they tend to sell poor bikes in general, let alone for people like us that put those components much more to the test.
My 1st piece of advice is to NOT spend $1000+ on a bike.. I don’t recommend dropping a huge amount of money until you’ve proven to yourself that you really enjoy it and remain committed to it. There are also a lot of other factors and expenses like the threat of theft, needing pricy bike lock, of course you’ll need a helmet, maintenance tools etc.
When you research a good bike, look up bikes friendly for ‘clydesdales’ it’s cyclist terminology for heftier riders. I recommend finding a local bike shop near you and going in for a visit, and perusing their used section. You can get a great used bike for a fraction of the cost of new.
2nd piece of advice, Is contrary to popular belief a lot of those larger, padded seats are actually NOT more comfortable. Now, of course YMMV. But the reason this is is because the primary place your weight is supposed to positioned on a bicycle seat is on your sits bones (you can google to see what I mean) that’s the real reason commuter/long distance bikes tend to have such scrawny seats. If you can get a seat that mostly lies on your sits bones you’ll have a lot less pain over time. Now keep in mind, at our weights that doesn’t mean NO pain, but I was shocked when I learned this and shopped around for skinnier seats over time. A lot of those more padded seats can seem more comfortable in the short term, but after even a couple minutes you really feel the strain.
If you find a nice bike shop in a good location they’ll often let you go out back and trial out bikes/seats (mine let us go in the back alley and ride different bikes around to get a feel before our purchase).
Now, if you don’t listen to ANY of my other advice above, one big thing that I haven’t seen mentioned that helped my gf and I (around 300+lbs) IMMENSELY is PADDED BICYCLE SHORTS! They are such a huge lifesaver. For some reason padded seats didn’t really help but the padded shorts have the padding at the perfect location to really help the strain + it helps prevent thigh chafing etc. Also, we found shorts online in our size and even larger on Amazon.
Another thing, not sure where you live but before making your decision I highly recommend scoping around and finding the flattest location you can find to start. If you’re not super active already, you’d be surprised how difficult even the slightest incline can be when you get started. You’ll be pleasantly surprised how nice it feels to be moving with the wind in your hair etc.
Okay, I know this got long, but my last piece of advice if you do move forward, is make sure you have basic tools for your bike with you at ALL times! My SO and I always bring a backpack with a multitool etc. This is good advice for any cyclist, but especially when you’re heavier there are little things that can go wrong with your bike at any time, and you don’t want to be stuck hoofing it when that occurs. (For example a common issue may be your seat losing its height over time with your weight and needing to manually adjust and retighten the bolts, or your peddles coming off etc.).
Anyways, sorry for the novel but I just remember how stressful it was for us making this decision and hope that any bit of this is helpful to you on your journey <3.