Techtool Pro 12 will be released this Fall, and will support macOS 10.15 Catalina. In the meantime, here are the known issues with Techtool Pro 11 when run in Catalina. In short, it is best not to use any Tool that will modify your disk (i.e. Volume Rebuild, Volume Optimization, Partition Repair)

Techtool Pro 11 Tests and Tools status when used with Catalina

Tests

Check Computer - Appears to work as expected. See below for individual tests.
Memory Test - Appears to work as expected.
Surface Scan - Appears to work as expected.
SMART Check - Appears to work as expected.
Partition Map - Appears to work as expected.
Volume Structures - Needs updating. Does not support the Read-Only system partition.
Video Memory - Appears to work as expected on some machines, but doesn't appear to draw correctly on others.
File Structures - Needs updating. Does not support the Read-Only system partition.
Fans Test - Appears to work as expected.
Battery Check - Appears to work as expected.
Bluetooth - Appears to work as expected. 
Network Interfaces - Appears to work as expected.

Tools

eDrive - Needs to be updated to create a functional eDrive.
TechTool Protogo - Needs to be updating to create a functional Protogo device.
Partition Repair - Appears to work as expected.
Volume Rebuild - Needs updating. Does not support the Read-Only system partition.
File Optimization - Appears to work as expected for Mac OS Extended (HFS+) volumes. APFS volumes are not supported for this tool.
Volume Optimization - Appears to work as expected for Mac OS Extended (HFS+) volumes. APFS volumes are not supported for this tool.
Volume Cloning - Needs updating.
Data Recovery - Appears to work as expected with HFS+ drives. 
Wipe Data - Appears to work as expected. 
Internet Speed - Appears to work as expected.
System Maintenance - Appears to work as expected.
Cache Rebuild - Appears to work as expected.
Volume Journaling - Appears to work as expected.
Home Permissions - Appears to work as expected.
Processor Check - Appears to work as expected.
Local Network - Appears to work as expected.
Video - Appears to work as expected.
Audio - Appears to work as expected.

 

Techtool Protection

All protection functions appear to function as expected.