Imac Late 2012, (macos catlina) crashes when typing

Welcome to Apple Support Communities.

I believe we need to proceed with an EtreCheck report. EtreCheck is a useful App to diagnose and identify issues, both hardware and software. It is trusted by many users. Please follow the steps outlined below:

1. Navigate to: https://etrecheck.com and get the free version of EtreCheckPro.
2. Download it. It is a free and trusted app. It is often recommended here on Apple Support Communities. 
3. Open EtreCheck, and before running the report, be sure to check “Allow full Drive Access” at the bottom of the EtreCheckPro window.
4. Run the report, and put it in a post, as seen here: https://discussions.apple.com/docs/DOC-250000211. We will then examine the report for issues in your Mac.

-Jack

First, you don't have a Time Machine backup. It would be a good idea to set one up.

Next, you can do some "clean up". Follow the EtreCheck prompts to remove orphan files.

You also have the malware known as "MacKeeper" installed!

You also have other issues. Since your Mac has many software issues, I would suggest to perform an erase and re-install of macOS. However, this can only be done if all your files can be backed up to an external hard drive. To backup, "copy and pate" or "drag and drop" files you want to save. If you use Time Machine to backup, do not restore from the backup. Rather, setup your Mac as "new", then Restore items backed up with Time Machine on Mac - Apple Support.

When you are ready to erase and reinstall, follow this guide. Again, this will erase all data:

1. Verify all your data is backed up to an external hard drive using drag and drop or Time Machine.
2. Sign out of your Apple ID in System Preferences > Apple ID > Overview > Sign Out.
3. Shut down the Mac.
4. Turn on the Mac, and immediately press and hold Command + R until you see the Apple logo.
5. Once you are in macOS Recovery, verify you are connected to WiFi in the top right corner. If possible, connect directly to the internet with Ethernet. 
6. Go to Disk Utility.
7. IMPORTANT Select "View" in the toolbar > "Show All Devices".
8. Select your main hard drive or SSD. This will be the top, non indented hard drive. 
9. Click Erase, and input the following exactly:
10. Name: Macintosh HD
11. Format: APFS
12. Scheme: GUID Partition Map
13. Click Erase.
14. Quit Disk Utility
15. Go to the reinstall macOS app.
16. Follow the prompts, and install on Macintosh HD.
17. Once done, setup your Mac. Once setup, drag and drop or copy your files back to the Mac, or restore certain files with Time Machine.

-Jack