Thanks for that clue about OS CA certs, I think that is involved. I did some research and it turns out that the Qnap NAS OS that Dokuwiki is running on doesn't seem to have a trusted certificate store for curl or wget, so if Dokuwiki Igor is trying to contact the plugin repository using those tools over https it would fail:
https://www.andreadraghetti.it/install-root-intermediate-certificate-bundles-on-qnap/
Wget provides a slightly more descriptive error than curl:
$ wget https://update.dokuwiki.org
--2022-11-20 10:40:39-- https://update.dokuwiki.org/
Resolving update.dokuwiki.org... 138.201.137.132, 2a01:4f8:172:3483::2
Connecting to update.dokuwiki.org|138.201.137.132|:443... connected.
ERROR: cannot verify update.dokuwiki.org's certificate, issued by ‘CN=R3,O=Let's Encrypt,C=US’:
Issued certificate has expired.
To connect to update.dokuwiki.org insecurely, use `--no-check-certificate'.
$ wget --no-check-certificate https://update.dokuwiki.org
--2022-11-20 10:41:24-- https://update.dokuwiki.org/
Resolving update.dokuwiki.org... 138.201.137.132, 2a01:4f8:172:3483::2
Connecting to update.dokuwiki.org|138.201.137.132|:443... connected.
WARNING: cannot verify update.dokuwiki.org's certificate, issued by ‘CN=R3,O=Let's Encrypt,C=US’:
Issued certificate has expired.
HTTP request sent, awaiting response... 200 OK
Length: 20 [text/html]
Saving to: ‘index.html.1’
index.html.1 100%[===================>] 20 --.-KB/s in 0s
2022-11-20 10:41:24 (4.31 MB/s) - ‘index.html.1’ saved [20/20]
Regardless though, it begs the question what changed between Hogfather and Igor in the way that it tries to contact the plugin repository that this even matters? Did it go from using a download method/API internal to Dokuwiki to calling out to OS native tools to download? Just guessing here. There is definitely no man in the middle or proxy server in my case.