Lightroom Cr3 problem

It would be helpful if you could post a copy of your System Info. You can obtain same from the LrC Help > System Info menu item as shown in attached screenshot.

Another thought about why there are lags while editing is that sometimes this is caused by an old or out of date or wrong graphics driver. So try installing the latest Studio graphics driver for this GPU. Since Nvidia offers both Studio and Game drivers for their GPU, make sure you have the Studio driver and not the game driver.

You haven't mentioned the cameras the files come from - always a good idea to do so, as it's obviously relevant. 

Are the CR3s significantly bigger than the CR2s?

If the CR3s were full-sized R5 files, and the CR2s are from a 10D (say), some slight degree of slow-down would not be a major shock. 

I'm also working with .CR3 files and I don't see such lags.

The first thing that you should try is to switch off the GPU support from the Lightroom preferences and check if that helps to fix the issue.

Go to Lightroom > Preferences > Performance tab > Uncheck "Use Graphics Processor" > Restart Lightroom.

https://helpx.adobe.com/lightroom-classic/kb/troubleshoot-gpu.html

Another step is to try to reset the Lightroom preferences.

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

It's recommended to backup your preferences before you reset the preferences to the default settings:

https://helpx.adobe.com/lightroom-classic/kb/preference-file-and-other-file-locations.html

If this doesn't help we need more informations about your environment.

Please provide also a copy of your 'System Info'. This can be get from the LrC Help > System Info menu item.

There's a copy button in the System Info dialog. Press this button and paste the info into your next forum post.

Pc:

I7-11700K

64Gb 3200Mhz RAM

RTX 3070

Asus B560-Plus