Is it safe to drive on the Trans Canada highway end of December from Calgary Airport to Banff National Park?

Unless there is a major blizzard, yes it is safe. I live 20 minutes away from Banff and I only use the Trans Canada to get to Calgary no matter what time of year. The highway is well maintained and very rarely too dangerous to drive on. December usually isn't bad for road conditions anyways, it gets really bad in late January to February.

YES the main road across Canada is well maintained between Calgary and Banff.
Do storms happen? Yes they do.
The snowplows clear the roads and life continues. In winter it is common to have snow. It is common to have snow plows too.
Banff is a very nice place with many special events for Christmas and New Years. Book Early it can get expensive for the best events.
Plan on 2-3 hours travel time late December. It can be less on nice weather day about 90 minutes Airport to Banff Hotel.. YOU DO NOT have to drive. There is shuttle bus service to Banff and Banff does have bus service to many of the tourist places.Ski slopes have buses to the Banff Hotels.
Suggest you take the ring road Highway 201 from the Airport less traffic congestion.
Check road conditions BEFORE you leave the Airport.

Highway 1A through Cochrane takes about 20 minutes longer than TCH. It is a two lane road and a very pleasant drive.A little easier for the driver to enjoy the view and not just the bumpers of the cars in front of you.
https://511.alberta.ca/region/Southern%20Alberta#:Alerts

https://www.banff.com/banff-airporter/

Yes. They plow it and salt it, but you should drive for the conditions, like going slower than the legal speed limit.

Lots of people do that safely. A few don't. Much depends on the weather at the time. It also depends on the skill of the driver.

Yes, the Grizzlies are hibernating by the end of December.

Last time I was there there were masses of road works around the airport badly signposted with ever changing speed limits and cameras. Don't get a fine as soon as you leave the airport.

Unless you are an experienced winter driver and can cope with sub zero temperatures, white outs and ice covered roads NO.