Hello,
Seems that icingadb/icingadb-web brings a lot of changes for third party related products.
Nagstamon is one of them, so I’ve opened an “issue” on github’s project there.
[Feature request] Add support of icingadb-web · Issue #822 · HenriWahl/Nagstamon (github.com)
Hope that the support of icingadb will become a reality one time.
If you are interested, you can follow that issue 
BR
FYI, icingadb support has been added in the latest nagstamon prerelease: Releases · HenriWahl/Nagstamon · GitHub