The Fifth Circuit decision holding that federal law invalidates (preempts) state laws that permit absentee ballots received some number of days after Election Day to count if they are postmarked on or before Election Day is not likely to be applied to this election. But some have raised concerns that suits like these are designed to delegitimate the election results, as part of a political effort to challenge the integrity of the election after votes have been cast.
I took a look to see which, if any, swing states permit absentees to be received after Election Day. Based on this website at the National Conference of State Legislatures, the only one is NV. In that state, absentees can be received up to 4 days after Election Day if postmarked by Election Day. NV also permits ballots with unclear postmarks to be received up to 3 days after Election Day — lower courts upheld this provision, which the RNC has challenged, and the NV Supreme Court heard argument on the issue on Oct. 8th.
The Republican Party also brought a separate federal lawsuit arguing that NV’s rule permitting receipt of ballots up to 4 days after Election Day, if postmarked by Election Day, violates federal law. This is the same issue the Fifth Circuit just decided. The NV suit was dismissed on standing grounds, and the case is on appeal to the Ninth Circuit.