Is there any new info on the Save Data bug?

Personally, I do run into occasional issues/bugs, but nothing has ruined my saves in this manner you seem concerned about. If I were you I would not live/play in fear of this... or let it stop you from playing. However, I must say that I would always, always recommend that you keep several backup saves of your game, just in case of any number of problems. I keep several saves that are recent, plus I keep several that are not as recent. I save them on my computer, preferably in two places... one on the computer or your backup drive, then one in an additional location, perhaps a thumb drive or second backup/external drive. I actually do this with all files that I would be sad to lose or that are important. For myself, I actually save the entire 'The Sims 4' folder from Documents > Electronic Arts > The Sims 4. At the least you will want to save/backup the following folders: Saves, Tray, Mods, Screenshots, Recorded Video, as you could add these folders to a new game install if yours became corrupted. There is a bit more info here if you want to know what those folders contain, etc.

You can play another/copied save file safely if you make two separate save folders. Just save the original The Sims folder somewhere as a backup so it stays safe and untouched in case the copied one you play with will come across some problems. 

To my knowing how the problems can spread is if you start new games in main menu (so you have several saves in one folder) and you switch from corrupted save to another save from main menu without closing the game in between. 

I'm on console.

if I build then it starts making rooms into rentals and assigning them the colors when its just normal residential and build mode stops working properly. My file is 7+ years old, there's too much to lose

Do you have the "Businesses & Hobbies" pack? There is a setting to assign areas in that pack also, while on residential lot type. Do you have the room assignment icon toggled to off (the icon pointed to by the red arrows in the screenshots below)? Also, what do you mean specifically about build mode stopping working properly?

Set to on.

Set to off.

I have all of the DLC- but it started happening specifically after For Rent. And it just stops functioning like I place a wall/ window or roof and it makes the sound as though I placed it but it doesn't. When I restart the game it starts working again and sometimes when I load in all of the things that were invisible are visible

LittleLeonette​ Hello! I did some testing on PS5 but I wasn't able to replicate the issues you described for a regular Residential lot; no colored lines indicating separate units.  I did encounter some problems with build mode for the Residential Rental lot type.  Please provide some more details so that we may be better able to help you.

• Double check the lot type to see if it's Residential or Residential Rental.
• For the lot you are attempting to edit, is it one that you built or is it from the Gallery?
• If it is a Gallery lot, is the lot type set as Residential or Residential Rental on the Gallery?
• Do you have a household that owns the lot / currently living there?
• Did you enter Build mode from the map view or from Live mode?
• Are you receiving any error messages when you attempt to place walls / windows or roofs?
• Any extra details you can provide about the steps you've taken will be really helpful.

When I tested this, I started with a Residential lot.  I tried Build mode from the map first.  Then I moved in a household and went to Build mode from Live mode.  There were no assigned units for either method.
Then, I converted the lot to Residential Rental.  Once a unit was assigned, I was not able to edit the unit while it was Hidden.  This was true for Build mode from the map and from Live mode.
After that I added a tenant and was unable to edit the unit at all.
I also tried converting the unit from a Rental back to a Residential.  I still did not have any assigned units / colored outlines.

I tried to build from scratch today in Brindleton Bay and it was working fine until I tried to "Move Lot" then the whole house turned pink. No Sims live there. Its residential. In order to get it to stop showing up with color I changed it to Haunted House Residential and then back.

No error message and I entered from the map. 

Could this thread perhaps be what you are seeing happening? 
[BH] Tiny pink outline lines appearing while building | EA Forums - 12084435

LittleLeonette​ Thank you for the extra details!  I tested this and can confirm this happened in my game both on PC and on PS5.  When I tried to move the lot, I got a pink outline.  When I exited to the map and reloaded the lot, the pink outline was gone.  I captured a video of this which also shows that the lot is Residential.
https://youtu.be/q4DITKuQTt0

I will note that it didn't happen when I tried to move a house / single structure in build mode, only when I tried to move the entire lot.  

I added my video to the thread that rosemow​ shared as well.