Install PuTTY ver 0.76 on Ubuntu 20.04 & comms to ESP32
You can install putty 0.74 from the Ubuntu 21.04 archive.
Download putty:
https://packages.ubuntu.com/hirsute/amd64/putty/download
and putty-tools:
https://packages.ubuntu.com/hirsute/amd64/putty-tools/download
Then navigate to the ~/Downloads directory and run:
sudo dpkg -i putty*
Possibly you can pick putty 0.75 from Ubuntu impish instead, but I haven't confirmed that that version is installable on 20.04.