It’s legal for a Texas resident to smoke weed in Colorado.
This is what they asked (although not very clearly) and the answer as you said is yes.
I think it’s also legal for Texas to make a law that’d allow them to arrest someone for travelling to Colorado with the intent to smoke weed
It's not. It's literally unconstitutional. Even Kavanaugh got that part right.
In his concurring opinion in last year’s ruling overturning Roe, Supreme Court Justice Brett Kavanaugh contemplated whether states could restrict their residents from getting abortions in other states: “In my view, the answer is no based on the constitutional right to interstate travel,” he wrote.