error compiling 2.1.0

[ostroffjh]

I already have kddockwidgets 2.1.0 installed, but my Gentoo system is telling me I need to reinstall it (@preserved-rebuild) but installation fails, I presume to some change in the toolchain perhaps being less permissive about something I don't understand.
Upgrading libfmt from 11.0.2 to 11.1.1 seems to have decreased the number of errors, but still gives:
/usr/include/fmt/base.h:2240:29: error: passing 'const fmt::v11::formatter' as 'this' argument discards qualifiers [-fpermissive]
/usr/include/fmt/base.h:2240:29: error: passing 'const fmt::v11::formatter' as 'this' argument discards qualifiers [-fpermissive]
(with 11.0.2 there were about a dozen similar lines)

I'm attaching the full build.log using 11.1.1.
build.log

Let me know what else I can try or other info to provide (or if I should have reported elsewhere)