Since the new dspNexus system will have an internal RPi4B running Buster for use, decided to get one to try out. This will work with the dspMusikLCD as it exists, so also applicable to that system. Have tried it on both the RPi3B+ and RPi4B systems and works correctly.
After loading Java 8, installed Room EQ Wizard latest beta version and everything is working correctly. Earlier versions of Raspbian had problems with some sample rates for REW. Buster has corrected that.
Connected the Dayton Audio UMM-6 USB mic to the RPi4B and it is running. REW shows the mic and could load the mic calibration data.
Only thing left to try is the noise generator with the internal DAC to see if it is working. USB DAC's externally have already worked.
Now a very small but very accurate way to measure room acoustics.