Twice the size would mean at least twice the gravity - probably more since "mostly" diamond is far more dense than "mostly" rock

Srs question, could an avg human walk against 2x gravity? Is that just 1G? Forgive ignorance

No, you are not taking into account relativity. Sure, from the perspective of someone back on earth your trip will take a super long time to cross the galaxy- longer than anyone’s lifespan- even if you are traveling at near the speed of light.

But I saidfrom your perspectivein that post, as in from the perspective of you on this hypothetical spaceship. Time dilates and length contracts for fast moving vehicles. If you are moving at a velocity v with respect to someone, to get the proper time in your frame of a trip that they time to be t, you will use the correction factor sqrt[1-v^2/c^2] to get t*sqrt[1-v^2/c^2]. Notice that as v gets arbitrarily close to c, that factor sqrt[1-v^2/c^2] gets arbitrarily small.

You could theoretically travel across the entire galaxy in a few seconds....if the speed was close enough to the speed of light [it would have to be ultra close].

The average human would probably struggle because they are unfit, weak, and fat af. But with proper training and adaptations they could. If you are 185 lbs, picture walking around with a barbell that is that same weight (might be easier than this due to weight distribution). Most people with a year or two of serious strength training could probably do this.

Studies in mice have shown in a 2G environment, muscle and bone mass increase to adapt to that new environment

also 3900 degrees on that planet, nothxjeff

Actually if the planet is 8 times as massive as earth at 2x the radius, the density would be about on par with earth, since volume scales with the cube of radius.

Wikipedia however lists a slightly different value for radius, 1.875 earth radius, but also with a mass of about 8 earth masses (density would still be close to being on par).So you would weigh 8/(1.875^2) = 2.28 times as much on the exoplanet than earth, if those stats are accurate.

Interestingly, the wiki article seems to say that it’s not even really certain what the characteristics of this exoplanet are yet, and whether its composition includes a large chunk of diamond- it may, but it appears this is not totally known.Better to see what the science is actually saying than go by sensationalist articles.