Canon EOS R3 Advanced User's Manual page 931

AE lock meter. mode after focus
For each metering mode, you can specify whether to lock the exposure (AE lock) once
subjects are in focus with One-Shot AF. The exposure will be locked while you keep
pressing the shutter button halfway. Select metering modes for AE lock and add a
checkmark [ ]. Select [OK] to register the setting.
Restrict shooting modes
You can restrict the shooting modes available with the <
Select available shooting modes [
< > to add a checkmark [ ]. Select [OK] to register the setting.
Caution
Restricted shooting mode settings are not registered to [
The [ ] mark cannot be cleared from all nine modes at the same time.
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> button.
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], [ ], or [
], then press
].