As I understand it, the GDPR is all about not using personal data in ways
not previously agreed and about understanding where there is a risk of data
beaches accruing and performing a risk assessment. So using a public Wi-Fi
in its self is not in breach of the GDPR. You would have a problem if
there was a data breach and you have been found not taking adequate
measures to secure your clients personal data.
Public Wi-Fi do not encrypt the data between your machine and the Wi-Fi
base station, so there is more of a chance that someone can grab the data
stream. This is slightly mitigated by the fact that QuickBooks uses https,
which encrypts your the data between your browser and the servers at Intuit.
In general it is never advised to use a public Wi-Fi spot for sensitiveness
data, without taking steps to secure your connection. Security people
often recommend the use of VPN software to secure your connection.
I have used ProtonVPN (for personal use), and I've also heard good things
about tigerVPN, both which work on multiple platforms, and whom have
privacy policies that mention the GDPR (I haven't read it thoroughly
Saying all this, when I have been this situation (only once lucky) I used
my phones 4G network, by setting up a Wi-Fi hotspot with a strong password,
actually turned out to be faster than the broadband I had at the time :-)