What carrier are you on? Some have "highly recommended" it and some haven't needed to at all.
If you're in the US, Verizon and T-Mobile have seemed to be the ones of concern:
Verizon seems to be mostly affecting their 5G UWB service. I moved my already-active 4G SIM over with no problem and got 5G: Section 5:
https://www.verizon.com/support/4g-sim-card-faqs/
Initially T-Mobile said for 5G, everyone would need the R15 SIMs, but now they've backtracked and said TM9263s are fine, too:
https://www.t-mobile.com/support/devices/latest-sim-for-great-network-experience
TM9263 and R15 dropped support for 2G devices, so there is a bit going on behind the scenes when it comes to differences in SIMs.
Of course, carrier stores may or may not have gotten the latest communications on the matter or may be sharing bad information, so that can't be helping either. I suspect if one is using an older SIM on either carrier, they may have some trouble with 5G.