I was searching for something else and came across this.  This has been a problem for years.  I don't know if it's been fixed because for many years now we do the following: 

We use the prior year program to set all our appointments.  All the clients are there anyway.  Even the ones who maybe took a year off that you didn't proforma.  We install the calendar as a stand alone icon and pin it to our task bar.  So, when users are making appointments in the 2021 calendar, it doesn't affect the speed and performance of 2022 Lacerte. 

It does feel weird that we are always a year behind on the calendar but we've been doing it for 5+ years with great success.  I'm sure some firms are bigger and it would be hard to communicate this to everyone but we have 9 preparers with 4 front desk staff and set roughly 4,500 appointments per year and it's been very smooth since we started doing that. 

Good luck!