On O2 the following devices have both a plastic sim slot and esim capability:
iPhone XS Max, XS, XR, 11, 11 Pro, 11 Pro Max, SE 2020, 12, 12 Pro, 12 Pro Max, 13, 13 Pro and 13 Pro Max
Samsung Galaxy S20 4G, S20 5G, S20 5G Plus, S20 Ultra 5G and Z Flip
Samsung Galaxy Watch Active2 and Watch3
Google Pixel 3 and 3 XL
Microsoft Surface Pro X.
I notice you have the Ultimate Oomph package with VM, you might be able to switch that to the Ultimate Volt package which uses an O2 sim, however I don't know if you would be able to swap that number over to an e-sim, but worth asking O2 about it.
EDIT I just noticed you have the S21 which isn't listed above, however they are adding add additional esim ready devices as manufacturers release them.
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