Starting in January, our software installers and updates on Windows will be signed with a new extended validation certificate issued by GlobalSign. For a smooth update experience past this date, we advise our users to update to Remote Desktop Manager 2023.2.34 or more recent.
Should RDM display an “invalid certificate” message when attempting to install an update, select the option “Download update using your default browser”. The packages are safe to install. As a security precaution, RDM includes a list of accepted certificates to ensure the updates are distributed by Devolutions (a method named certificate pinning).

https://docs.devolutions.net/kb/remote-desktop-manager/troubleshooting-articles/invalid-certificate-error-updating-remote-desktop-manager/
Sébastien Duquette
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Just to inform you. I also get this error with versions after 2023.2.34. I still have 2023.3.37 and receive the error.
Hi Tom,
Sorry for the inconvenience. I would like to verify some details with you to help us pinpoint the source.
Sébastien Duquette
FYI - Once I got up tot 2023.2.39 using the "download with default browser", update went smoothly.