I agree with your comment, it is often an overlooked topic. Inlining icons can be one answer but be aware of the growing size of your DOM. Depending on the complexity, number and repetition of the icons you are using, an approach including lazy loading can be better. Layout shift is first and foremost caused by an improper space reservation.

https://lucide.dev/

I really like https://phosphoricons.com/

But other than that, I also usually default to Material UI Icons.

https://www.svgrepo.com I find the site very user friendly as it lets you customize the stroke's width, color etc, see how it looks like and copy the modified version.

I’ve used FlatIcon extensively. My use case is video games rather than web design.

https://www.flaticon.com/

I like Material Symbols best. Largest selection AFAIK and simple enough that you can create unique ones that fit in.

famfamfam of course, the only set one will ever need

Honestly, I always default to material icons unless a project calls for a very specific style. The coverage is just so dang good I rarely find a scenario without an appropriate icon and the style is neutral enough to blend in with a number of UI designs.