[Full Changelog](https://github.com/vector-im/element-web/compare/v1.7.20...v1.7.21-rc.1) * Upgrade to React SDK 3.14.0-rc.1 and JS SDK 9.7.0-rc.1 * Translations update from Weblate [\#16427](https://github.com/vector-im/element-web/pull/16427) * Add RegExp dotAll feature test [\#16408](https://github.com/vector-im/element-web/pull/16408) * Fix Electron type merging [\#16405](https://github.com/vector-im/element-web/pull/16405) * README: remove Jenkins reference [\#16381](https://github.com/vector-im/element-web/pull/16381) * Enable PostCSS Calc in webpack builds [\#16307](https://github.com/vector-im/element-web/pull/16307) * Add configuration security best practices to the README. [\#16367](https://github.com/vector-im/element-web/pull/16367) * Upgrade matrix-widget-api [\#16347](https://github.com/vector-im/element-web/pull/16347)