Pretty sure they're not.

US tax brackets seem to be

https://www.irs.gov/newsroom/irs-provides-tax-inflation-adju...

1% inflation seems about right for the 2020->2021 tax year. Most indicators are lagging so if inflation started taking off during 2021 it wouldn't show up right away.

That shows nothing about the amount of the adjustment. Looking up last year's and running a few calculations, it appears to have been adjusted 1%! That's not adjusting for inflation. Not sure what it's adjusting for, but not inflation.

Headline literally says

IRS provides tax inflation adjustments

And links to https://www.irs.gov/pub/irs-drop/rp-20-45.pdf

"This revenue procedure sets forth inflation-adjusted items for 2021 for various provisions of the Internal Revenue Code of 1986 (Code)"

It's states adjusting for inflation for the tax year beginning March 2021. The document came out in October 2020 when inflation was 1.2%, I'm not sure when they adjust it and you may disagree with the measure of inflation

The year before was November 2019

https://www.irs.gov/pub/irs-drop/rp-19-44.pdf

Here's the one for 2021/2 (Nov 29th 2021)

https://www.irs.gov/irb/2021-48_IRB

Married Individuals Filing Joint Returns, lowest and highest bands:

Thresholds for tax year 2021/2 goes from 19750 to 19900 (0.7%) at one end, and from 622050 to 628300 at the other (1%)

Thresholds for tax year 2022/3 goes from 19900 to 20550 (3.27%) at one end, and from 628300 to 647850 at the other (3.11%)