What about an encrypted email service...? No endorsement, but I use ProtonMail. There are varying levels, I pay for a subscription, but there's a free service, too. It's end to end encryption, from the client side. It's based in Geneva, Switzerland, which is totally neutral and free from any regulations on privacy (Switzerland isn't in the EU). Your relative doesn't have to have ProtonMail, you can send emails to their regular email address.
A free ProtonMail account also gives you 1GB free ProtonDrive storage, so that could be another option. The file wouldn't be decrypted until your relative downloads it onto their computer. The team behind Proton met at CERN (y'know the team looking for the Big Bosom...err, Higgs Boson...) so they have decades of experience between them. https://proton.me/about.
I subscribed because I believe that privacy is - or at least should be - a fundamental human right, and Switzerland has some of the strictest and most stringent privacy laws on Earth.
I also find Proton's tech support extremely friendly, knowledgeable and helpful.
I would sign up for a free ProtonMail account and then upload the file to your free ProtonDrive storage. You can then send the link to your relative who can then download the file. Little bit of extra legwork then sending it direct, but nobody will be able to read that file unless you give them permission (and it's all very James Bond, as the links will self-destruct in 30 seconds. Not really, but they are degradable, for obvious reasons).
Is that a solution, or is it too techie for you (I know it would be for my parents - although if that's the year you were born, you're a fair bit younger)...? If you need help, Proton's user community is brilliant (in every sense).
