Welcome to the forum @Svend_Age_Brink
How complex is the dependency? The most documented way to do something after a backiup is to use Scripting options such as run-script-after. See Example Scripts. Script might use command line though.
Export As Command-line can help with that. You can, of course, do a series of jobs from a single script.
Credential exposure in scripts can be handled somewhat by access permissions on the script, or by a parameters-file, or possibly even by passing in from a run-script-before (done as securely as you wish).
A simple schedule can also sometimes be done by relying on Duplicati server only running one at once. Second job waits, and runs when first is done. Challenge is setting order of missed schedule jobs, and seemingly it’s top to bottom on the job screen. It’s hard to change that order without a job export/import.
duplicati-client talks to the server, thus is subject to the same one-at-a-time rule. Command line can run several jobs at the same time, each independently of each other and of whatever server (if any) is doing.
Some previous discussion:
Complex backup sequence?
In what order does missed backup jobs run?
Change the sequence of backup jobs done
is sort of an unknown, but whatever it can add will presumably be a Duplicati Inc. add-on to the open core.