Itās perfectly fine for the post_max_size and upload_max_filesize limits to be different. One affects the amount of data which can be added in the $_POST data, the other controls how much data can be passed to the $_FILES data.
Googling the error message, the first result I see is this one:
In it, they say that the post_max_size should be equal or greater than upload_max_filesize. This is the case on our servers too (10 MB upload size, 20 MB post size). So this is all good.
If Site Health says this is not OK, thatās a problem with the Site Health plugin. The support thread also concludes this.