Here's Secretary Yellen's letter discussing the IRS funding in the Inflation Reduction Act stating that new funds are not to be used to increase the audit risk for businesses and individuals under $400k relative to historical levels.
You don't even have to trust her word here. It is the most efficient use of new IRS funding. The easy low-income taxpayer audits are already done. They are largely automatic correspondence audits by mail. What have been lagging over the years amidst chronic understaffing are audits of wealthy taxpayers as those require resources to do.
Low-income taxpayer audits have high tax revenue per audit hour, but only as a consequence of not requiring many audit hours to do. Wealthy taxpayer audits generate a substantial amount of tax revenue, but require more audit hours to do.
To put it another way with audit enforcement, the IRS could increase field audits of low-income taxpayers, but it wouldn't be very rewarding on a per audit hour basis.
Correspondence audits by mail take no time and yield relatively large revenues (say if a reporting mismatch detected a W-2 wasn't properly filed). But a field audit of that same taxpayer probably isn't going to find much underreporting as that taxpayer likely only has W-2 income.
Meanwhile a field audit of say Trump or Exxon could find lots of underreported income.
This is of course why field audit risk isn't equal among taxpayers. Generally self-employed taxpayers are audited relatively more than those that are W-2 employees. New businesses tend to be audited more than older businesses. The IRS has limited resources, so it approaches distributing audit enforcement efficiently (there is a research audit that has a random distribution across taxpayers for the express purpose of helping the IRS understand where to target its audit resources).