the reason the inventory looks worse on bedrock is that the vanilla resources are bugged. there are a few resource packs that fix it, if you're into that sort of thing.
item frames on bedrock edition are block entities and not just regular entities, so they can't have mob effects.
pressure plates should be very easy to make invisible by just setting their blockshape to "invisible" in blocks.json, though this is something i have not tested. i don't think blockshapes work on item frames.
it's probably something to do with one of the resource packs. if looking into the files isn't an option, try disabling them one at a time to see which one it is
placing blocks mid-air is not a feature and never has been. the feature that makes bridging easier on bedrock is the ability to bridge forward, which is available on all releases of bedrock edition. you will have to change your 'control mode' to 'joystick & aim crosshair' in order to be able to hold down the place button.
villager trades were not changed in 1.21 except that cartographers can now sell trial explorer maps. the villager trade rebalance is not yet an official feature of the game and is locked behind an experimental toggle.
i don't know this for certain, but the items are probably given using a function, so, theoretically, you could probably use a function to clear the player's inventory after this. but idk enough about functions to help any further.
try going to video settings and scrolling down until you see a slider labeled 'anti-aliasing'. you're going to want to make sure this is slid all the way to the left. it's going to say it's set to '1' when you do this, but it's actually going to turn it off, which is what you want.
what are your settings like? bedrock edition has an option for anti-aliasing and it's set to 4 by default for some reason on certain platforms. that might be causing the framerate issues.
hmm.... there would be a lot of factors if i had to pick only one, but i'd probably go with bedrock. java edition's lack of controller support basically makes this no contest.
if the pack's uploaded in .mcpack format, you should just be able to run the file and the game'll import the pack on its own. otherwise, you just need to unzip the file and move the resulting folder into one of bedrock's many resource pack directories (if you don't know the difference between them, just use the main one).
i don't remember off the top of my head if creepers support transparency by default, but if they don't, you can go into the creeper's client entity file and change the material to one that does. i know "skeleton" supports non-partial transparency, and i think "slime" might support partial transparency but i'm not super sure on that.
