Is there a way to make spellcheck not mark numbers that start with a decimal point (".22") as an error? AKA: Any way to disable "Reversed Space and Punctuation?" error?

The use of a proceeding decimal without a 0 in front (for example: “.22”, not “0.22”) is common for many technical subjects and even casual use (.6 ounces), but LibreOffice marks this as an error (“Reversed Space and Punctuation?”). I can make the current document ignore this by simply right clicking and clicking ignore all, but the issue returns next session. Is there any way to make it always ignore this?

For example
“While .380 ACP and .45 ACP continue to see common use, .25 ACP and .32 ACP now make up less than 0.75% of US ammo sales.”

It is Grammar check, not spell check, that is flagging the issue.
You might be better to use the Middle Dot, U+00b7, for such use rather than a full stop as it is clearer to read ·22 than .22
You could either set up the calibres in AutoCorrect to have .22 (or :.22:) change to ·22, or do a Find and Replace afterwards. There must be only a limited range. Or even have some combination such as -. change in AutoCorrect to a Middle Dot
BTW using .6 ounces risks error, it is the reason that 0.6 ounces should be used as there is no reason to have a leading 0 except to show that there is a decimal point and it cannot be confused with 6.

The title should be a short summary of the question. Also add relevant tags in addition to writer.

That’s not helpful in the slightest. The first idea violates the styling that has been used for over a century. The second adds more work than hitting ignore every session.

In USA apparently according to Wikipedia.
In the Commonwealth countries decimal points were not full stops, they were middle dots until the 1960s which is why I, in my parochial manner, suggested a mid dot as being a familiar sight. Sorry to have offended you so much.
Of course, you don’t have to hit ignore, you can just ignore the blue grammar indicator, it doesn’t print and is not exported to PDF.