Existing apps for digital signatures generally require converting a document to PDF format, followed by drawing "boxes" where signatures and other information from signers will go. Since 2022, I have been collaborating with serial entrepreneur Eric Warnke to create an easier solution. Using a Google workspace add-on, we allow document owners to add fields directly to the document, and then collect signatures by emailing signers a secret URL.
The entire process requires no authentication (beyond Google), and no storage of personal data.