The gas usage for simple transactions like transferring of native tokens on Ethereum as well as Polygon remain 21000 gas units mostly, but it can increase during periods of high network congestion.
However, you can specify any gasLimit as long as it's within the constraints of the block gas limit, as transactions must fit within the block gas limit to be included in a block. You can read more about this from here:
https://ethereum.stackexchange.com/a/161698/91017
So, if you specify the gasLimit as 21000 (or don't specify at all, as it's the default) for transferring of ether (i.e., native token), then it'll utilise 100% of that as gas usage. Like this:

And, if you specify the higher gasLimit (say 50000), then most of the times, it'll utilise only 21000 (unless there's some network congestion, high usage or so), and the remaining gas will be refunded to you, like this:

21000in Ethereum not static? – kriss100 Mar 19 '24 at 20:05