Waiver by an appellee?

Many opinions address briefing waiver issues by an appellant. But what about an appellee? The Fifth Circuit examined that procedural point in Texas Democratic Party v. Abbott:

“Appellate rules regarding how we treat absent issues differ depending on whether it is the appellant or the appellee who has neglected them. An appellant can intentionally waive or inadvertently forfeit the right to present an argument by failure to press it on appeal, a higher threshold than simply mentioning the issue. On the other hand, even an appellee’s failure to file a brief does not cause an automatic reversal of the judgment being appealed. By appellate rule, so extreme a lapse does cause the appellee to lose the right to appear at oral argument. Fed. R. App. P. 31(c). We also know that if we disagree with the grounds relied upon by a district court to enter judgment but discover another fully supported by the record, we can affirm on that alternative basis.  . . . There are a few cases that consider rules of waiver even for appellees. For example, our discretion to consider an argument not properly presented is ‘more leniently [applied] when the party who fails to brief an issue is the appellee.'”

No. 20-50407 (Sept. 10, 2020).