(LPT) Debian 12 Latency spikes/unexpected real time delay. Looking for solution.

As written in the first post, first uninstall the current LinuxCNC with:
sudo apt purge linuxcnc*

After that install all the deb files, I think that placing these deb files in a separate folder and entering: sudo apt update && sudo apt install ./*.deb will be the easiest way. Otherwise like in the first post

Just started and i have to post because this is a good example how it always goes for me:
1. sudo apt purge linuxcnc*
works, buty doesnt remove Linuxcnc because: (Package 'linuxcnc' is not installed, so not removed)

cncpc@debian:~$ sudo apt purge linuxcnc*
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Package 'linuxcnc' is not installed, so not removed
The following packages were automatically installed and are no longer required:
libwpe-1.0-1 libwpebackend-fdo-1.0-1 linux-headers-6.1.0-18-amd64
linux-headers-6.1.0-18-common linux-headers-6.1.0-18-common-rt
linux-headers-6.1.0-18-rt-amd64 linux-image-6.1.0-18-rt-amd64
Use 'sudo apt autoremove' to remove them.
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

Linuxcnc is of course installed. I dont get it, but thats standard for me already:)

I am planning to do a fresh debian 12 install and delete everything what is currently on the system.
Do i understand correctly, after Debian 12 is installed, i need to do this:
sudo dpkg -i (package name here without brackets)
for each deb that is here onelaboratories.us/abc/ and after that reboot and choose the rtai kernel in grub?

Its just unbelievable... why god damn it cant work..
What i did:
1. fresh install of debian 12
2. downloaded every file from onelaboratories.us/abc/
3. went to downloads folder and opened a terminal
4. first i tried "I think that placing these deb files in a separate folder and entering: sudo apt update && sudo apt install ./*.deb will be the easiest way"
NOT WORKING - if i remeber correctly, something is missing
5. then i tried this: sudo dpkg -i (package name here without brackets)
5.1: i started with: sudo dpkg -i linux-headers-5.4.290-rtai-amd64_5.4.290-rtai-amd64-1_amd64.deb
5.2: sudo dpkg -i linux-image-5.4.290-rtai-amd64_5.4.290-rtai-amd64-1_amd64.deb
5.3: sudo dpkg -i rtai-modules-5.4.290_5.3.3-linuxcnc_amd64.deb
5.4: sudo dpkg -i linuxcnc_2.9.4_amd64.deb

Dont ask me why in this sequence. I just did that because no where its described with which deb to start.
As you can see on the pictures there are things missing.
I then tried to open Latency test fom the drop down (xfce) menu but nothing happend, then i opened terminal and wanted to open it through command.You can see the result on the last pictures.

Guys, please tell me what i did wrong.

UPDATE:
i did again a fresh install of Debian 12 and did the same as described in my previous post with sudo dpkg -i (package name here without brackets).
I then opened Synaptic pacakge manager and it showed me a broken package, which was linuxcnc. I clicked on it and did complete removal. Then i updated everything that synaptic made available and then again i did sudo dpkg -i linuxcnc_2.9.4_amd64.deb.
When i do Latency-test, the pc freezes.

I dont get it, but this is the best example of why i just hate linux.

If i did something wrong or without a sequence, then i need to remember, that the only information i got from first post of forum.linuxcnc.org/9-installing-linuxcnc...debs-for-2-9?start=0 , is that i have to have Debian 12 installed, without Linuxcnc.
Then i download the DEBs of onelaboratories.us/abc/linuxcnc_2.9.4_amd64.deb
and each of the 4 DEBs i need to install by "sudo dpkg -i (deb name)".

This does not work.
On start up of the machine i get for about 2 seconds the information that you can see on the attached picture.

Try this
forum.linuxcnc.org/9-installing-linuxcnc...-2-9?start=40#308037
And follow from there on.
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Getting permission denied from apt is strange, especially since you are correctly running as a normal user.
In about 90% of cases, if you get this error, one of the memory modules is on the way out, so it might be time to dust off your PC and check the memory.
If you do have another PC, you can install everything there and move the drive after finishing to this PC, that almost always works properly with Linux. Almost for me is 1 failed boot in about 500.