I use 1Password with my elderly MIL but she finds it confusing. Even though she has been using computers for 30+ years and a Mac for 15+ years something about the process of clicking the 1P icon in the browser bar or going to 1Password to copy a password frequently trips her up. She will try to remember or write down the password and manually enter it into whatever field she's been prompted to fill.
As for why we use 1Password instead of iCloud Keychain: my spouse and I are routinely tasked with helping my MIL log into sites, so we have set her account to default to saving to a shared vault we each have access to (we have a separate 1Password family account to share between my spouse and I).
We briefly tried a Yubikey and other biometric options and ran into what is apparently a common problem for elderly people: she has barely perceptible fingerprints. She could not use Touch Id on her iPhone when that was a thing and cannot reliable use it on her 2022 MacBook Air.
I hate to say this but shifting to a long, memorable passphrase (reused across sites) coupled with a second factor may be more useful for an elderly user.
