A fact checking article says that these are found in all corpses and are a result of... dying. Not from covid, not from vaccines. They're part of the death-decay process.
https://factcheck.afp.com/doc.afp.com.34KB4DG (this is a French news source that does fact checking in France... so... no American/US influence there.)
So: a little fact checking, then.
The claim comes from "a Thai neurologist"... so, someone who doesn't do autopsies. Neurologists are experts in many things but they are NOT experts in what happens to a body at death and afterwards (that's a pathologist.)
A lot of the information is based on "claims" -- but there's no record of who they were studying or which death certificates and autopsies that show proof of their proposal. This is important -- claiming something doesn't mean it's true without some hard data to back it up. I can claim that herds of buffalo are eating up all the grass and destroying my lawn, but I'd better be able to show buffalo poop, tracks, hair, and photos to prove it's buffalo and not wild hogs.
Anybody can show you a photo of an agar plate or something under the microscope and say "this is Thingy X." People tend to believe this without stopping to think "is this something real?" -- particularly when the information is presented in a video (it's well known that video presentations engage your emotions more than text does, and when your emotions get engaged, your brain may not go on a deep fact-checking dive.) None of the people promoting this stopped to ask some critical questions:
- What's the source of this "stuff under the microscope"? (who died, what was the cause, how long has this thing been sitting around?)
- You say it's being found by funeral directors... but they don't do autopsies. And they don't pull stuff out of the body. (fluids, yes, and the state of those fluids depends on a lot of things: https://www.shermanschapel.com/embalming)
- WHICH funeral directors (and where) are these things being found? (are the customs of the country related to this -- because the length of wait before embalming (if any) is done would change things)
- under what conditions is this "stuff" seen? Is it seen in the living, for example?
(etc.)
So we have a single statement by someone who doesn't do autopsies about an unspecified number of cases that he "says" happened (no statements from the people saying this or the number of people who said this, etc.) that sparked an Internet wildfire of sharing.
On the opposite side, we have
So... I recommend doing homework. In this case it does get difficult because the literature is for scientists and it's ... it's a long, difficult, and somewhat dull (very precise) read and you'll do a lot of dodging around through dictionaries to figure out what some things mean.
For myself, I agree with the French there (having checked their work) that the whole thing is bunk.