I'm looking for a cloud based, self hosted, FOSS application for design

As it says in the title…

I’m seeing some nice web based design apps (eg: Crello, Figma) but I need something I can install on my own domain (self hosted) and tweak to add functionality if I need to. Ultimately I want to engage my clients in online, collaborative design sessions. The designer will have access to full functionality, the client will be able to see what the designer is doing / creating as the designer does it, and the client will be able to use a pen type tool to freehand mark up the design on their end (or erase stuff they draw). The designer can also see the clients markings. For example the client might draw a circle around some element of the design and then comment on it, or they might draw an arrow pointing to something and comment on it, or they might erase something they had drawn on the design and the designer can see this and respond. Anything is appreciated. Does anyone know of a free and open source resource that can be downloaded, installed, and is cloud based / accessible over the web - or am I on my own here?

Thanks in advance for any help.

Jake