Need help picking a destination with a $4k budget / 10 days

FINALLY have a decent amount of money saved for a short trip somewhere (4k not including flight because I know flight prices change). 10days including travel so about 7/8 days touring.

$1500 max to spend on air bnb (I also have 75k chase points I can use for hyatt if I need extra).

$2500 is for transportation, excursions, tours, food etc

Looking to go between sep-end of October because I want to avoid flying during holidays but can't go anywhere over summer. This will also give me time to extend my budget but for now im at $4k.

I prefer somewhere warm. I would love a beach destination but can live without it just as long as it's between 70-90 degrees (im in Nevada).

I'm open to anything either adventure or just relaxing in a nice park, lakes, mountain etc.

I've never been international so please help me find a beginner friendly city. Something walkable, quick train rides or non scammy ride share.

My biggest concern is obviously safety since I'll be alone and a new traveler.

I'm also concerned about food poisoning. I'm a huge foodie and love dining out but if you have a horror story about food poisoning please lmk because that's a nightmare.

Also open to hopping to another city 4 days in one & 4 days in another or all in one.

Am I way under budget? Please help! I'm overwhelmed and don't know where to start.

So far I've researched koh Samui, tulum, London, Bahamas and Lisbon.

Not interested in Costa Rica, Bali or Cancun.