I'd assume that self-hosting is not an option for this user?

Otherwise the alternatives would be pretty much a nobrainer for me:

Microsoft Office 365 -> Nextcloud Bitwarden -> self-hosted Bitwarden/Vaultwarden GitHub -> Sourcehut/Codeberg/Gitea/Forgejo Google search -> Searxng Reddit -> Lemmy Hackernews -> Lobsters Twitter/LinkedIn -> Mastodon / any Fediverse software