artefacts after raw file is opened and still present after export

The artefacts are in both modules, Library and Develop. They are similar but not identical.

On your rig, in LrC, do these artifacts so up in both Library Module and Develop module, or just Library?

Lightroom Classic-Version: 10.0 [ 202010011851-ef6045e0 ]
Lizenz: Creative Cloud
Spracheinstellung: de
Betriebssystem: Windows 10 - Business Edition
Version: 10.0.19042
Anwendungsarchitektur: x64
Systemarchitektur: x64
Anzahl logischer Prozessoren: 24
Prozessorgeschwindigkeit: 3,7 GHz
SQLite-Version: 3.30.1
Integrierter Speicher: 65479,5 MB
Für Lightroom verfügbarer phys. Speicher: 65479,5 MB
Von Lightroom verwendeter phys. Speicher: 2296,4 MB (3,5%)
Von Lightroom verwendeter virtueller Speicher: 2930,2 MB
Anzahl GDI-Objekte: 717
Anzahl BENUTZER-Objekte: 2423
Anzahl Prozess-Handles: 2209
Cache-Speichergröße: 3,4MB
Interne Camera Raw-Version: 13.0 [ 610 ]
Maximale Anzahl Threads, die Camera Raw verwendet: 5
Camera Raw SIMD-Optimierung: SSE2,AVX,AVX2
Virtueller Speicher in Camera Raw: 883MB / 32739MB (2%)
Physischer Speicher in Camera Raw: 954MB / 65479MB (1%)
DPI-Einstellung des Systems: 120 DPI
Desktop-Komposition aktiviert: Ja
Monitore/Anzeigegeräte: 1) 2560x1440
Eingabetypen: Multitouch: Nein, integrierte Toucheingabe: Nein, integrierter Stift: Nein, externe Toucheingabe: Nein, externer Stift: Nein, Tastatur: Nein

Informationen zum Grafikprozessor:
DirectX: NVIDIA GeForce RTX 2070 SUPER (27.21.14.5730)

Anwendungsordner: C:\Program Files\Adobe\Adobe Lightroom Classic
Bibliothekspfad: D:\Lightroom\Standard\Standard-v10.lrcat
Einstellungen-Ordner: C:\Users\kunes\AppData\Roaming\Adobe\Lightroom

Installierte Zusatzmodule:
1) AdobeStock
2) Facebook
3) Flickr
4) Nikon Tether-Zusatzmodul

Config.lua-Flags: None

Adapter Nr. 1: Anbieter : 10de
Gerät : 1e84
Subsystem : 551019da
Version : a1
Grafikspeicher : 8011
Adapter Nr. 2: Anbieter : 1414
Gerät : 8c
Subsystem : 0
Version : 0
Grafikspeicher : 0
AudioDeviceIOBlockSize: 1024
AudioDeviceName: Lautsprecher (High Definition Audio Device)
AudioDeviceNumberOfChannels: 2
AudioDeviceSampleRate: 48000
Build: LR5x42
Direct2DEnabled: false
GL_ACCUM_ALPHA_BITS: 16
GL_ACCUM_BLUE_BITS: 16
GL_ACCUM_GREEN_BITS: 16
GL_ACCUM_RED_BITS: 16
GL_ALPHA_BITS: 0
GL_BLUE_BITS: 8
GL_DEPTH_BITS: 24
GL_GREEN_BITS: 8
GL_MAX_3D_TEXTURE_SIZE: 16384
GL_MAX_TEXTURE_SIZE: 32768
GL_MAX_TEXTURE_UNITS: 4
GL_MAX_VIEWPORT_DIMS: 32768,32768
GL_RED_BITS: 8
GL_RENDERER: GeForce RTX 2070 SUPER/PCIe/SSE2
GL_SHADING_LANGUAGE_VERSION: 4.60 NVIDIA
GL_STENCIL_BITS: 8
GL_VENDOR: NVIDIA Corporation
GL_VERSION: 4.6.0 NVIDIA 457.30
GPUDeviceEnabled: false
OGLEnabled: true
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GL_ARB_explicit_attrib_location GL_ARB_explicit_uniform_location GL_ARB_fragment_coord_conventions GL_ARB_fragment_layer_viewport GL_ARB_fragment_program GL_ARB_fragment_program_shadow GL_ARB_fragment_shader GL_ARB_fragment_shader_interlock GL_ARB_framebuffer_no_attachments GL_ARB_framebuffer_object GL_ARB_framebuffer_sRGB GL_ARB_geometry_shader4 GL_ARB_get_program_binary GL_ARB_get_texture_sub_image GL_ARB_gl_spirv GL_ARB_gpu_shader5 GL_ARB_gpu_shader_fp64 GL_ARB_gpu_shader_int64 GL_ARB_half_float_pixel GL_ARB_half_float_vertex GL_ARB_imaging GL_ARB_indirect_parameters GL_ARB_instanced_arrays GL_ARB_internalformat_query GL_ARB_internalformat_query2 GL_ARB_invalidate_subdata GL_ARB_map_buffer_alignment GL_ARB_map_buffer_range GL_ARB_multi_bind GL_ARB_multi_draw_indirect GL_ARB_multisample GL_ARB_multitexture GL_ARB_occlusion_query GL_ARB_occlusion_query2 GL_ARB_parallel_shader_compile GL_ARB_pipeline_statistics_query GL_ARB_pixel_buffer_object GL_ARB_point_parameters 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Please post your System Information as Lightroom Classic (LrC) reports it. In LrC click on Help, then System Info, then Copy. Paste that information into a reply. Please present all information from first line down to and including Plug-in Info. Info after Plug-in info can be cut as that is just so much dead space to us non-Techs.

I downloaded the raw file and saved it as a JPEG on my Windows 10 computer. It did not display the artifacts that are displayed in your JPEG. There is definitely something wrong with your system.

Building on Jao's reply, after disabling the GPU but before doing any further editing, do Preferences > Performance > Camera Raw Cache Settings > Purge Cache, just in case some of the previous corruption has made it into the cache.

And definitely run a memory diagnostic.  LR uses much more memory than most other apps, and memory failures can affect LR but not other apps you run.

[Use the blue reply button under the first post to ensure replies sort properly.]

Downloaded your raw file and imported into Classic. I do not get the artefacts visible in your jpeg file on my MacBookPro. The image looks just fine. Something about your system is causing this and I would indeed suspect the graphics card or your system memory. Have you tried turning off the graphics acceleration in Preferences->Performance? Your post didn't explicitly mention it. It is interesting that camera raw in Photoshop does the same thing for you which would point to something related to graphics card drivers.

The link with all informations ist my Microsoft Onedrive, so no risk klicking the link. This is the jpg exported from the raw format. Raw files cannot be uploaded (or I don´t know how to do it).

I certainly will not click on your link to an unknown web site. To include photos in your message, use the "Insert Photos" button here in the Adobe Support Community, and then we can see what you are talking about.