The speed of your internet connection can be influenced by factors like network congestion, the priorities set by your carrier, and the quality of coverage in your area.
If you've manually configured the APN settings for your eSIM and they aren't accurate, it might seem as if your connection is sluggish.
Often, the underlying issue could be a misconfiguration during eSIM installation.
As a quick fix, toggle the airplane mode on and then off.
Should your eSIM be compatible with various carriers, consider shifting to an alternative one.
If the issue persists, you might want to revisit and adjust your APN settings or temporarily switch to a 3G connection via Cellular > Voice and Data settings.