"Can't" isn't really the right word, but it's unlikely. A general rule of thumb is people tend to place roughly a full tier below where they ended the previous season at as a side effect of the soft reset, but it's all mmr based and doesn't actually care about your final rank.
People who end the season with mmrs worse than their ranks might suggest usually get a bit of a shock when the get placed waaay below where they were expecting even if they do good in placements (e.g. previous season silvers getting placed B5 even with a positive winrate in placements), and similarly those with mmrs above what their rank would suggest can end up even placing higher than they ended at (although again this is unlikely, since the soft reset tend to pull people down).
Accounts that have never ranked before start with a silver 4 ish mmr, which means getting their mmr up to plat 5 level (or higher) is super impractical since they only have 10 games to do so, and can only duo with gold ranked players at best, which leads to the plat 5 'best'. In theory though, a top tier challenger player could make a smurf, win and dodge a ton so they never actually get promoted past gold, and end up with a challenger mmr despite being gold ranked. If a fresh account then duo'd with the gold ranked player with challenger mmr, and proceeded to still win all 10 placement matches (despite likely facing plat/diamond-ish players), it seems theoretically possible that the fresh account could get placed as high as plat 1 which is the highest anyone can place.
This is of course not at all practical, but the point is it's all mmr based at the end of the day, so if after the reset+placement matches your mmr is gold, you'll get placed gold, regardless of what your end of season rank was.
(Sometimes people get to gold 5, and then semi-troll or don't take things seriously since they earned their rewards and it's really hard to be demoted tiers so they don't think it matters. They still destroy their mmr though, and then get a harsh awakening when their 'gold 5' account gets placed bronze, since again, mmr is what matters, not rank.)