I think the line:
{% set fan_on_temp = printer.configfile.settings['heater_fan hotend_fan'].heater_temp|float %} in fan_tach_monitor.cfg may need to be changed to
{% set fan_on_temp = printer.configfile.config['heater_fan hotend_fan'].heater_temp|float %} for newer versions of Klipper.
20210821 - https://www.klipper3d.org/Config_Changes.html
At the time of writing, this stopped the error, but I haven't actually checked it works yet :) I'll be back soon with an answer.
I think the line:
{% set fan_on_temp = printer.configfile.settings['heater_fan hotend_fan'].heater_temp|float %}infan_tach_monitor.cfgmay need to be changed to{% set fan_on_temp = printer.configfile.config['heater_fan hotend_fan'].heater_temp|float %}for newer versions of Klipper.20210821 - https://www.klipper3d.org/Config_Changes.html
At the time of writing, this stopped the error, but I haven't actually checked it works yet :) I'll be back soon with an answer.