Using an esim card?

Yes, they work. I have successfully used Airalo eSIM twice in France, also Portugal and Germany. Download the app and follow the instructions, it's simple. Your phone must be unlocked to use an eSIM.

Check that your phone allows you add an eSIM. We have iPhones in my household. My husband's phone doesn't allow him to add esim because it is "locked" (he got through our phone provider). Mine is unlocked, so I have not had any issues.

You keep your original phone line, but you get a new data plan for cell phone service. You don't get a new "number".
Once you are traveling, you switch your settings for cell service to use data from the eSIM plan. I remember the first time it took me a bit to understand which setting to change or keep. And I use wifi when available.

I have used the eSim from Nomad for a few years now. They have country specific and also regional plans. I've used successfully in Scandinavia, Europe, Morocco and South America.

We use Airolo.; I recommend buying a $5 local esim to practice loading it, turning it on and off, etc. Their tutorial video is good.

The idea of a practice run with a local eSIM is a good one if you have a tightly scheduled itinerary and every minute is going to count. However, I've learned from experience that the installation instructions for at least Airalo's eSIMs can vary somewhat from country to country. They are never difficult, and they are clearly explained, but you do have to read and follow the specific instructions provided for each country. It doesn't necessarily work to follow the same steps in Country 2 that a US eSIM might require (voice of experience here).

I am not the world’s most tech savvy person but this YouTube video (https://youtu.be/Pi1Cb1tEeSI?si=vH5IVj9bt2fqXJCd ) made installing an Airolo eSIM so easy for me. I would suggest watching it before purchasing one just to get the idea of what to do. Keep in mind it is a couple of years old, but the gist should be the same if not identical.

Good advice.
A small nit to pick:
A SIM card is a physical card, it's inserted into a slot or a little carrier in the phone
An ESIM is not a card, it's a bit of data downloaded from the seller, and stored in a special place in the phone. The data is normally loaded into the phone by taking a photo of a QR code provided by the seller.

When you look at a vendor's website, sometimes they will sell both SIM and ESIM. Be sure you chose the one you need.