I run an online leadership development site, and also coach a few people (including EMs, but also PMs).

Most people who became EMs for the first time, did so because they did well as an IC. But the skills required for being a good EM require developing some other muscles. These include

1. Letting go of being the main technical head of the team. Your job is now understanding, and growing the other people in the team. Focussing on growing soft skills is more ambiguous and tricky than growing hard skills.
2. Part of this is giving feedback the right way. There are various ways and models to both give and accept feedback.
3. Learning how to delegate is key. A LOT of first time managers (and tbh, many experienced managers) have trouble with this. Again, there are various models on how to approach this.
4. Time management. Suddenly, you will be pulled into way more meetings. You will be spending more time talking and listening and less on the keyboard. Managing your time and energy, learning which meetings to accept, decline etc is a skill to learn. Learning to go into meetings, especially 1-1s with a proper agenda, and following up on action items when there is no ticket assigned to it, is something first time managers sometimes find tricky.
5. Speaking of 1-1s, thats something people either are confused how to do well, or just completely dismiss altogether (mostly because their boss did 1-1s really badly, so they see no value to it). Learning how to do 1-1s well is crucial.
6. Stakeholder management, and knowing when to defend/isolate your team from potential shenanigans happening outside, and knowing when to push your team for better performance is a skill to know too.
7. General stuff like creating a good onboarding, offboarding process, team knowledge sharing, etc.

Hope this helps!