Chromium

As a workaround, I have a userscript that sends web share data to the clipboard / downloads. Surely the browser could provide at least that much on Linux?

(function() {
    'use strict';

    if (!navigator.canShare && !navigator.share) {
        navigator.canShare = (data) => true;
        navigator.share = (data) => {
            const {title, url, text, files} = data;
            const body = [title, url, text].filter((element) => element).join('\n');
            let promise = body ? navigator.clipboard.writeText(body).catch((error) => {
                console.log(error);
                alert(body);
            }) : new Promise(undefined);
            if (files) for (const file of files) {
                promise = promise.then(() => {
                    new Promise((resolve, reject) => {
                        setTimeout(() => {
                            try {
                                const url = URL.createObjectURL(file);
                                const a = document.createElement('a');
                                a.href = url;
                                a.download = file.name;
                                document.body.appendChild(a);
                                a.click();
                                document.body.removeChild(a);
                                URL.revokeObjectURL(url);
                                resolve();
                            } catch (error) {
                                reject(error);
                            }
                        }, 500);
                    })
                });
            }
            return promise;
        };
    };
})();