You can find the compatible ISSCBTA drivers through specialized driver archives, as official manufacturer support for these older chipsets is often discontinued:
Microsoft tightened driver signing after Windows 10 version 1903. Fix: Permanently enable Test Mode: Isscbta Bluetooth Driver For Windows 10
Installing the Isscbta driver on Windows 10 can be done through several methods: You can find the compatible ISSCBTA drivers through
Note: Modern versions of the Toshiba stack are sometimes paid software or restricted to Toshiba laptops only. You may need to look for older, free versions of the stack archives on driver repository sites. Isscbta Bluetooth Driver For Windows 10
Windows 10 often includes signed ISSC drivers through Windows Update.