ATTINY1614 can only program for 16 Mhz or 20Mhz

[JohnRob]

I'm using a Dr Azzy ATTINY1614 dev board, with recently installed megaTinyCore. I can download via UDPI successfully, however I was under the impression that I could set the clock for any frequency shown in the "Tools / Clock" dropdown (see end of post). However only 20Mhz or 16Mhz internal clock settings work, with everything lower than 16Mhz setting the clock to either 20Mhz or 16Mhz.

Is this the limitation or am I missing something?

Thanks
John

20Mhz:
Version 1.2.3 - Jan 2022
Using serial port COM7 at 57600 baud.
Target: attiny1614
Set fuses: ['0:0b00000000', '2:0x02', '6:0x04', '7:0x00', '8:0x00']
Action: write

16Mhz
Version 1.2.3 - Jan 2022
Using serial port COM7 at 57600 baud.
Target: attiny1614
Set fuses: ['0:0b00000000', '2:0x01', '6:0x04', '7:0x00', '8:0x00']
Action: write

10Mhz
Version 1.2.3 - Jan 2022
Using serial port COM7 at 57600 baud.
Target: attiny1614
Set fuses: ['0:0b00000000', '2:0x02', '6:0x04', '7:0x00', '8:0x00']
Action: write

Similar to post:

ATTiny1614 Timer B issue

[JohnRob]

From:
https://github.com/SpenceKonde/megaTinyCore/issues/191

Yes, it's very easy!
Select the 3216/1616/... from tools -> board menu. Select the 8 mhz
internal option from the tools-> clock speed menu, and then do "burn
bootloader". When uploading, be sure to use the same setting for click
speed.

Background:
These parts use a different scheme for clock speed than the classic avr's -
a fuse sets whether the base oscillator speed is 16 or 20 mhz. It always
starts with that prescaled by 6, but the prescaler can be changed at
runtime; megaTinyCore does this (in init(), which is run at startup before
setup is called) to get the selected clock speed. See the readme for more
information.