@benlimanto, if you’re willing to, instead of XFCE’s WM, use ⪅ xorg-x11-server-21.1.16-1.fc41.rpm [1] with ⪅ kwin-x11-6.3.3-1.fc41.rpm, you can import a .KWinRules file containing noborderrule=2 into kcmshell6 kcm_kwinrules:
However, you might (hopefully, very temporarily) be unable to, if bugs.kde.org/show_bug.cgi?id=501810 affects more than merely me.
Additionally, none of this is advisable, because it’s XOrg-specific. However:
…it renders SSDs around the CSDs, so it shan’t break anything: [2]

