What can I plan for few hours in Salzburg, late evening ?

maybe its just me but I don't understand your itinerary?
if you are near Berchtesgaden ( great spot to stay BTW, so much to see nearby) and need something different to do at night, take your swimmers with you and try the therme.
https://www.watzmann-therme.de/en
its open til late. we did it last year and enjoyed it, met some locals and generally had a very relaxing time after walking in the national park near hintersee.
BTW there is a good 'park and ride' system if you want to get into Salzburg but don't want to find a park in the city. we did it last year.
hope this helps.

Sorry, if I was not clear. I was trying to give my overall itinerary. May be, that made my post confused.

I am reaching Freilassing around 4:30 PM. Instead of going to hotel (which can be around Berchtesgaden) and sleep, I want to utilize that evening. Outside Salzburg, it may be too late to visit at that time, so I am thinking to spend that time in Salzburg.

But most of places, I mentioned above, will be closing soon. Here I need help, how can I plan that evening in Salzburg.

Go to a bar. That's what I'd do. Have a drink with the locals.

Thats a nice idea Paul.

But I am restricted by short time in this area, so thought of utilizing this, either in or around Salzburg

Dinner at the Old Fox: http://www.alterfuchs.at/de
After dinner stroll down car free Linzer Gasse and cross Staatsbrücke and walk about Old Town.
Cross back over the bridge and check out the Hotel Stein rooftop bar: https://www.7-senses.at/en/morning-noon-night/

Thank you, will look at these options

The old town is worth exploring with your camera. It will provide you with many photo opportunities. Take the time to walk along the river toward the Augustinerbrau Mulln. It is a wonderful beer garden with delicious beer brewed only in wooden kegs. It is in the Rick Steves guidebook. I make it a point to get there every time I am in Salzburg. Get a Halbhendl, a liter, share a table with some locals and have a chat. It makes a lovely evening.

As I understood your suggestion, please correct me, if I am not.

Pick car from freilassing and park at Park Garage Linzer Gasse. Walk towards Staatsbrücke, roam around Old City Hall (per google map, I think this is old town area), Augustinerbrau Mulln and after dinner, back to parking.

Next day, I will be coming from Berchtesgaden. Should I again park at Park Garage Linzer Gasse which can be convinient location ?

Do not use highways ("Autobahn") in Austria unless you have a toll sticker ("Vignette") attached to the windshield.

The Linzergasse garage is reasonably close to the old town. The RS guidebook also explains a park-and-ride option with the bus. Perhaps you just want a relaxing evening in Berchtesgaden and tackle Salzburg fresh the next day. It would depend on your priorities and your interest level in Salzburg. I think the RS guidebook has a walking tour of the inner city--your enjoyment would depend on the level of daylight when you arrive for just the evening. Or just stay in Salzburg at least the one night so you can have your full liter of beer (or two) and not drive that night.