binaries dated 20200923 were built from the following sources:

zlib-1.2.11.tar.gz
bzip2-1.0.6.tar.gz
json-c df27756491abf9ecce648c3aa85d6a70feb4c600 (current master)
botan tag 2.15.0
rnp b9e32bfaf04bdc4d69d5902d55ddd44d638a8cd5 (current master)

with minor manual tweaks to make it build
(fixing build rules and some missing defines)

zip files signed with key
21D16E67E18398C8DA9DDF2E1C27423725007724

instructions:

unzip and copy all individual files directly to the directory containing thunderbird.exe

Rename the original rnp.dll file to a different filename, for example to orig-rnp.dll