Many scenaria, basically most that opens a new window with help from KDE plasma. Note that “new window” from Konsole or Chrome or others, does not exhibit this. I.e. the window appears “instantly” in that case.

this is perhaps the simplest example:

• From the command line, do “konsole“.
• The whole system gets unresponsive. I have a digital clock running, and the seconds stop counting.
• About 30 seconds later, the new Konsole appears, the seconds continue counting and the system unfreezes.

I tried “strace -t -o /tmp/strace konsole“, and this is what I see at the relevant moment:

...
08:21:00 munmap(0x7c8108167000, 147456) = 0
08:21:00 poll([{fd=3, events=POLLIN|POLLOUT}], 1, -1) = 1 ([{fd=3, revents=POLLOUT}])
08:21:00 writev(3, [{iov_base="22613j3", iov_len=12}], 1) = 12
08:21:00 futex(0x7ffc7dbe9448, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL,                     FUTEX_BITSET_MATCH_ANY) = 0
08:21:32 futex(0x563396bd8218, FUTEX_WAKE_PRIVATE, 1) = 0
08:21:32 fcntl(8, F_GETFD)              = 0
08:21:32 fcntl(8, F_SETFD, FD_CLOEXEC)  = 0
08:21:32 poll([{fd=3, events=POLLIN|POLLOUT}], 1, -1) = 1 ([{fd=3, revents=POLLOUT}])
...

So, 32 seconds of wait for some futex condition. I tried some googeling but it doesn’t see to lead anywhere, so can anyone help me getting forward?
Sometimes the problem goes almost away (2-5 seconds wait) after running the booted system a day or two, and sometimes rebooting helps (for a while). So it is kind of random.

Details:
Host: Windows 10 Enterprise, 22H2
Vmware: VMware® Workstation 17 Player, 7.5.2 build-23775571
Guest: Ubuntu 24.04 LTS / Noble
Operating System: Kubuntu 24.04
KDE Plasma Version: 5.27.11
KDE Frameworks Version: 5.115.0
Qt Version: 5.15.13
Kernel Version: 6.8.0-31-generic (64-bit)
Graphics Platform: X11
Processors: 12 × 12th Gen Intel® Core™ i9-12900H
Memory: 20,6 GiB of RAM
Graphics Processor: SVGA3D; build: RELEASE; LLVM;
Manufacturer: VMware, Inc.
Product Name: VMware Virtual Platform
System Version: None

I was expecting the new konsole to show up a bit faster.