Might not remember much of anything
This is where the problem lies. Anything that requires you to have some knowledge or memory might fail. Anything that does not require some knowledge or memory is something that ANYONE else could do and therefore take your bitcoin.
If... lets say, you kept it in a steel container with instructions
Will you remember it's in a steel container? WIll the container be hidden in a way that you can find it?
If finding it requires memory of it, then you might not remember. If finding it does not require memory of it, then someone else may find it.
any way to make sure the people freezing you dont just take it?
Only if you can count on having a memory of it.
Or if they dont, what if you wake up, and you dont realize what you have?
Yep. You either need to trust someone with the info (in case you forget), or you need to trust that you'll have memory.
Maybe I could put on on stainless steel, like a thin sheet, scratch the seed phrase in, then have it shoved in my arm or leg and stitch it up, then die, wake up.
If they search your body before freezing you, they'll likely find it (especially if they xray you first).
Maybe have some sort of instructions that would only make sense to me in the event i forget about it...
And if you forget the thing that allows those instructions to make sense to you?
or..... maybe like... I put it in an awkward place in my arm or leg so it's guaranteed to give me some major issues and will need removed so it will remind me. like if i forget my memories, I wake up, ouch my leg kinda hurts when i walk. go to doc, doc x rays and is like you got some random metal in your leg wtf lets remove it. on th metal, rolled up, it says "my name" or whatever to open only. no one else. then has instructions how to retrieve the btc?
You still have to hope that nobody discovers it in the freezing process and that nobody discovers it while you're frozen. You also need to hope that having a chunk of metal won't interfere with the freezing process and make it ineffective or severely damage the surrounding tissue.
Like go to a bank and be like hey, can I rent out the safe deposit box for the next 100 years?
Will you remember that you put something in the bank box? And if you do, the bank might go out of business 10 years before you are revived and all contents of unclaimed boxes are destroyed?
Anything that requires knowledge, requires you to remember something. Planning under the assumption of a loss of memory means planning for the possibility that you are a completely different person, meaning that a completely different person can access it.