I have a dual-SIM phone with AT&T and T-Mobile lines (a Google Pixel). I wish they had a triple-SIM phone, then I could add Verizon.
Now that I think about it, I think you can have multiple eSIMs, but only one can be active at a time.
FWIW, in my Galaxy S23U I can put 2 physical SIM and 10 eSIM.
iPhones support 8 (or more): https://support.apple.com/en-us/118227#:~:text=You%20can%20h...
Unsure why they say 'or more' and what makes that happen.
2 can be active at the same time.
I can't find how many a Pixel can store at the same time though.