Lag after upgrading PC

It shouldn't cause these issues, but try creating a new catalog and import a few of the same image files into it. See if it performs any differently.

I am using the catalogue file from my earlier installation. Could this cause some issues ?

I have a similar system using a much lower performance Intel 8700K with no issues. I doubt it's due to the AMD 5950x CPU.

Is this a homebuilt or prebuilt rig?

So, rethinking, one item in your SYS INFO

Displays: 1) 2560x1440

So you are not running 4K.

Now this was an issue with older GPU's (pre GTX 1000)

Turning on use Graphics Processor will not help sub 4K and may make things worse.

In your case

Graphics Processor Info: 
DirectX: NVIDIA GeForce GTX 1080 (30.0.14.7111)

so right about the point just after that was a highly likely concern

Your 5820k was effectively a high-clock quad channel memory Xeon with some features disabled and 28 PCIe lanes and lots of cache.   The Ryzen is a desktop processor with dual memory channels and enough PCIe lanes for the video card, a single M.2 NVMe, and shared bandwidth for everything else which will mostly be eaten up by a couple of USB 3.2 devices.   Do you have any expansion cards aside from the GPU?  They're eating into its bandwidth.  Did you check the motherboard manual for which of the slots drop speed when something else is enabled?   Even on my former 5820k enabling the USB 3.1 ports on the board drops a PCIe slot from 4x to 1x.   There's a whole table of what speed goes to crap when you enable this or plug that in there and it was less constrained.   It's monumentally worse on desktop chips and hardware vs. the workstation level equipment Haswell-E was.    It's very likely that the effective performance of the hot new chip is worse, sorry to say.   Most of the target market for the new desktop processors are gamers, who would buy an original pentium and swear up and down it was awesome if you put RGB LEDs on it, so they get talked up a lot.

You really want threadripper or whatever intel is selling their gimped xeons as now for this sort of thing.  I ended up looking into it, couldn't afford the premiums, and picked up a refurbished 6950x for $300 on ebay which mysteriously benches a couple of % faster than the fastest new ryzen without accounting for the benefits of quad channel memory in 2 banks.  Honestly the new workstation i9 pseudoxeons weren't much better but they at least had ~50% on the 5 year old processor.  The threadrippers were insanely faster, obviously.   Yes I know I'm not being that helpful but it's something to strongly consider as a possibility.

In reviewing this post there is no mention of resetting the LrC Preferences file. When uinstalling and reinstalling LrC the current Preferences file is retained and not over-written. It can become corrupted and cause numerous unexplained issues. Follow the procedure at the below article to have LrC create a new default settings Preferences file. I suggest simply renaming the file Lightroom Classic CC 7 Preferences.agprefs.HOLD, which will allow restoring it if of no help. Try LrC again without making any changes to the default settings.

https://www.lightroomqueen.com/how-do-i-reset-lightrooms-preferences/

So, some performance tips for the OS and for the GPU.

see tip 8 in:

https://au.pcmag.com/migrated-15175-windows-10/5180/12-simple-tweaks-to-speed-up-windows-10

and for the GPU, NVIDIA Controll Panel, you want to modify the power management 

missing old link, but mgt described in:

https://www.techporn.ph/basic-nvidia-control-panel-3d-settings-optimization-guide/

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.

Sample below as of 7/1/2021
Lightroom Classic version: 10.3 [ 202105281559-8dc50eb4 ]
License: Creative Cloud
Language setting: en
Operating system: Windows 10 - Business Edition
Version: 10.0.19043
Application architecture: x64
System architecture: x64
Logical processor count: 8
Processor speed: 4.0GHz
SqLite Version: 3.34.0
Built-in memory: 16317.1 MB
Real memory available to Lightroom: 16317.1 MB
Real memory used by Lightroom: 1302.8 MB (7.9%)
Virtual memory used by Lightroom: 1586.9 MB
GDI objects count: 746
USER objects count: 2288
Process handles count: 1909
Memory cache size: 252.3MB
Internal Camera Raw version: 13.3 [ 807 ]
Maximum thread count used by Camera Raw: 5
Camera Raw SIMD optimization: SSE2,AVX,AVX2
Camera Raw virtual memory: 299MB / 8158MB (3%)
Camera Raw real memory: 303MB / 16317MB (1%)
System DPI setting: 96 DPI (high DPI mode)
Desktop composition enabled: Yes
Displays: 1) 2560x1440
Input types: Multitouch: No, Integrated touch: No, Integrated pen: Yes, External touch: No, External pen: Yes, Keyboard: No
 
Graphics Processor Info:
DirectX: NVIDIA GeForce GTX 1070 Ti (27.21.14.6089)
 
Application folder: C:\Program Files\Adobe\Adobe Lightroom Classic
Library Path: F:\Files\Pictures\Vacations and Day Trips\Photo Trips\24 Photo Trip September 2019\24 Photo Trip September 2019-v10.lrcat
Settings Folder: C:\Users\goldi\AppData\Roaming\Adobe\Lightroom
 
Installed Plugins:
1) Aurora HDR
2) ColorChecker Camera Calibration
3) DxO PhotoLab 3

Try doing a clean install of the lateset Nvida Studio Driver.

https://www.nvidia.com/Download/driverResults.aspx/176849/en-us