Based on the feature "publish, then review" also known as Post-Publication Peer Review (when used as formal review method) there are indeed alternative platforms:
-Open Research Europe https://open-research-europe.ec.europa.eu/ only researchers involved in projects or grants of Horizon 2020 and Horizon Europe are eligible to publish
-Gates Open Research https://gatesopenresearch.org/ is a platform for rapid author-led publication and open peer review of research funded by the Bill & Melinda Gates Foundation
-HRB Open Research https://hrbopenresearch.org/ is a platform for HRB-funded researchers to rapidly publish their research outputs in an open and accessible way
-Wellcome Open Research https://wellcomeopenresearch.org/ for as they state themselves “A new way for Wellcome-funded researchers to rapidly publish any results they think are worth sharing”
Examples of some individual initiatives using post-publication peer review are:
-Cureus https://www.cureus.com/about_publishing a stand-alone journal that is discussed here on RG https://www.researchgate.net/post/Cureus-publications-Worth-it-or-just-a-waste-of-time
-Sci https://www.mdpi.com/journal/sci a journal published by MDPI see also https://blog.mdpi.com/2018/07/23/post-publication-peer-review-for-sci/
-eLife https://elifesciences.org/ seems to have make the shift as well https://elifesciences.org/for-the-press/a4dc2f54/elife-shifting-to-exclusively-reviewing-preprints
Do keep in mind that this publishing approach is (still) somewhat controversial: