FCPX: huge rendering files

How to prevent FCPX to generate hi–quality media during file render? I edit short video and FCPX generates hundreds of GB of rendered file chocking my memory. I unchecked: "background render", "Create optimized media for multycam clips", in playbacks,"balance color", "Create optimized media", "Create Proxy media", fix audio problems" in Importand still see FPCX generating tons of files.  so, I am forced to delete them every 20-30min of editing.
I use FPCX for the last 8 years and never saw this problem until I installed new version 10.6.4 on new computer and started new project

Try resetting FCP preferences, as described in step 11 on this page:  support.apple.com/en-us/HT203477

You will of course have to manually re-enter the preferences you want. As a test, set FCP Preferences>Import>Files to "Leave Files in Place", and make sure you do not import using "Copy to Library". Also under Import settings make sure "Create Optimized Media" and "Create Proxy Media" are off.

Also make sure background render is off, Create Optimized Media for Multicam Clips, After doing that, create a test library, import some material and see if it automatically generates render files upon import.

I know you already did some of these but the FCP preferences can get messed up and behave erratically. Resetting them as above and re-entering the settings will often fix that.

If it still happens in a new test library after importing a few clips, make sure you are not applying any effects to the clips. If it does not happen on import but does happen when you add clips and effects to the timeline, in some cases a 3rd-party effect might cause it.

If you are using stabilization or optical flow retiming, FCP will create analysis files (not render files) but some of those can be large.

Thank you:
I started a new library with ne wpreferences (i.e. un-checked everything) and it helped in my old libraries.