There are five women in our department, but I always get all the difficult tasks. The others quickly tell the boss: “I don’t know how to do this” or “I’ve never done this before.” I usually can do it...

It sounds like you’ve become the reliable problem-solver in your department. That’s a good quality 👍, but it can also mean people depend on you too... much and give you the hardest tasks. It’s reasonable to want a fairer workload.
Here are some ways you can handle it without damaging your reputation:
1. Don’t say “I can’t” — say “I’m currently busy”
Instead of saying you don’t know how (which your boss may not believe), try saying things like:
“I’m currently working on another task. Who else could take this one?”
“I can start it later, but maybe someone else is available now.”
This shows you’re responsible but not always available.
2. Suggest sharing the task
You can respond with:
“Maybe we can divide it among the team.”
“This could also be a good opportunity for others to learn it.”
This gently encourages the boss to involve others.
3. Ask for priorities
If many difficult tasks come to you, ask:
“Which task should I prioritize first?”
Sometimes the boss will realize you already have eno more