[Imustaskforhelp]

Cryptpad comes to my mind although I suppose it might lack some features of google sheets but it has a web interface.

For a non web interface, things like libreoffice can be good too but I think that you are asking for a web version..

I am not sure if libreoffice has a web version, it seems that they do but I can't find much information and I might recommend crytpad personally so.