Yeah there was this old tweet from Bethesda that kind of confirmed it. Though I guess to be fair that could change. Most of their 1st party titles have had that option so I’d be surprised and disappointed if it didn’t.
yeah... and I just checked Skyrim and FO4 on the Xbox store. both of them don't have "Xbox play anywhere" and therefore no shared saves. so it's likely the same for Starfield.
And I get the thing about the mods. I was still hoping for cross platform saves, because I haven't really decided yet whether I want to play on Xbox or PC. and it would suck to start over again after having played for several hours on one platform.