General WebGL optimization advice?

I'm trying to evaluate whether I can use Unity for an upcoming web game project or I have to look to a dedicated WebGL platform. Sadly, my client insists I *must* support mobile browsers for this project, not build native apps. I understand Unity is not recommended for mobile, I'm trying to determine how strong that recommendation is.

My initial tests have been mixed.

I see a lot of threads here referencing optimizing, but I haven't found any general guide to what are the best steps to take. The game does not depend on a ton of gameobjects, particle effects, physics, or heavy textures and animations.

With mobile performance and load times in mind, what should I pay most attention to? What steps can I take to design the game to be as lightweight and performant as possible? I see people saying "use the package manager", but all I can remove in there is TextMesh Pro?

As an aside, I see there is a Unity for Instant Games in alpha ( https://unity.com/solutions/instant-games ), but it appears the "more info" link is 404ing?

Thanks in advance!