It can help to create some small routines that are easy to put in place. E.g. Have tea together and when you sit down, ask fun querstions like: if you had 1 million pounds to spend just on yourself, what would you buy? If you had a million to spend just on making the world a better place, what would you do with it? What is your dream house? Etc. You join in too. Share dreams and ideas. My young teens loved these questions and it actually can help you get an idea of what is important to them and what careers might suit them later on.
You could also ask for help in the kitchen after dinner - disco dishes - put on a dance track of music you know your teenage daughter likes and you have to clear up while dancing to it. You might feel stupid at first but once you all get used to it, it's fun.
Or you could bring your laptop to breakfast on Sunday and do Desert Island discs with your teen - ask them to choose the eight tracks of music that would keep them going on a desert island, and play them one by one.
It's fine to be knackered and watch TV after work. Do it together. Find some family shows to watch and discuss - go for uplifting stuff like Strictly or funny long running series like Parks & Rec rather than nasty, manipulative reality TV stuff like Love Island or IACGMOOH.
In the holidays, sit down with all yoru DC and make a holiday bucket list for each season. Encourage them to choose simple and cheap fun things. At Christmas it might be: Go for a frosty walk to look at lit up houses, have hot choc with marshmallows, have a family film pizza and popcorn night, decorate the tree, make paper chains, go to a carol service etc.
I did stuff like this because i had severe depression when DC were young and like you I wanted them to have fun. Finding easy things that didn't cost much money or effort but had lots of value was what worked best.
You sound like a lovely mum, by the way. I was so worried about my depression affecting them that I bust a gut to be 'fun mum' - OTT at times on reflection. The small things are what they love most.