Thanks for linking!
Do you only see the problem if Opus starts during boot and not if it is restarted afterwards? That may make it harder to track down, since the tool for detecting leaks works best if you launch Opus via the tool.
From your screenshot, I note that there's also CPU and disk access happening. Was the screenshot taken just after boot, before any Opus windows had been opened? If so, does it (and the memory usage?) stop after a while, or only once Opus is restarted? Process Monitor is a tool which can be used to see which files are being accessed, which may provide a clue as to what's happening.
The underlying issue could be many things, and may be something in Opus or something outside of Opus (e.g. antivirus scanning triggered by Opus checking the details of file collections at startup, then caching the result so it doesn't happen the next time). Shell extensions would normally be a big thing to consider, but less so if this is happening before any Opus windows are displayed. (Their involvement is still possible, but much less likely.) Finally, script add-ins and Opus plugins all do things at startup which may be relevant.
You may also want to try with Opus 11.13.3 beta or above, since we recently fixed a memory leak which would occur if the system environment variables were changed frequently. They are not normally changed a lot during boot, but it's possible your system has a tool which is changing them more than usual. If so, that fix should solve things, and it is not in the "stable" releases yet.