If the manufacturer has decided not to give a lens a tripod collar they’ve decided the weight of the lens shouldn’t stress the mount. The are even cases,like the Nikon 70-200 f4 where the tripod was not needed and therefore not included as a standard accessory, that Nikon made it available as an (expensive) optional extra. People moaned at first that it wasn’t it included but soon worked out they didn’t need it.
Looking at the weight data for both the Fuji camera and lens they are very similiar:
XT-4 607g
XF 70-300 580g
Im not a Fuji user but I wouldn’t be concerned by the lack a tripod collar on that lens. the manufacturer has decided not to include one by design so it shouldn’t cause any issues not having one.
I’m currently considering a switch to canon. The camera I’m considering weighs 598g and the lens (70-200 f4) weighs 695g. That doesn’t bother me because canon have designed it that way. If I was to get the 70-200 f2.8 version thats 1097g and comes with the tripod collar as a standard accessory in the box I’d use the tripod collar as they’ve decided to include it as a standard accessory. My feeling is if it’s provided use it, if it’s not don’t worry about it. The lens designers likely know far more about cameras and lenses than we do.
One of the best items you can get for a camera is a L bracket. It makes changing to portrait orientation when there is a tripod collar so much easier. It also keeps the weight of the camera/lens over the central pivot of the tripod.