How bad is a full suspension for commute?

I am buying a ebike with the tax benefit from my employer at some point this year.

Budget ~4000€

I have no deeper knowledge about ebikes and hoping someone help out a noob. I wonder what the difference between shimo motor and Bosh is, and if there is any and are other brands just worse overall? (I only see bosh and shimano bikes)

I want a mountain ebike and I would just it primarily for commute in the city environement (15km to my work) would 2.6" tyres or a full suspension be bad for it? Are the riding position usually designed for MTB only? I will do some hobby cycling in the forest also as extra exersize. I have no problem buying a front suspension one, but are there any recommendations in terms of brands to look for? I know trek and canyon, are they top tier?

Thank you in advace!