What I've found works best for me is:
- Seamly2D (https://seamly.net/) and Valentina (https://gitlab.com/smart-pattern/valentina) - these are two forks of an open-source project. They do pretty much everything I want them to do.
- Clo3D: https://www.clo3d.com/ - horrendously expensive subscription software ($50/month or $450/yr) but there are.. Uh... Less legal options available online. My favourite aspect of this particular software is that it lets you view the constructed object (usually a garment) in 3D and run physics simulations on it.
I've tried Optitex and Gerber as well but despite being the standard in industry, I don't find them to be great pieces of software. Of the two, Optitex is much better than Gerber but both are really hard to use.
I think Clo3D is probably the most approachable option but it does cost. Seamly2D/Valentina have a steeper learning curve than Clo3D but they're also much more capable when it comes to design and in particular, parametric design.
As purely a passing interest I recall trying to find a platform years ago but being disappointed with what I found.
I've always wanted to design the 'perfect' (for me) laptop bag but found the task daunting. This is coming from someone whose worked with Lasers/CNC Mills/CNC Routers/3D Printers/traditional mechanical & electrical CAD enough to be comfortable with the concepts of computer aided design and machine operation.