Inkscape, Adobe Illustrator & PowerPoint are good for these vector graphical abstracts. Inkscape is the free software. Here are some vector graphic tutorials for scientists on my channel DrawBioMed. https://www.youtube.com/channel/UCaj-dnHpfViQRv9-vQFl4Jw. If you have specific questions about certain structures, welcome to ask me in the comment section.
Graphical abstract drawing at very low cost (Starting price: 35 USD for 2D image) use the link: https://www.facebook.com/grapicmaster/ All you have to do is send a pencil drawing of your concept to be illustrated to them they will draw accordingly. Once drawn the graphical image of your illustration you can see the image and pay for it. It is very flexible and precise.
For sure you can use Mind the Graph to produce these figures. I use and recommend Mind the Graph. It's online software that you can use for free or with a subscriber plan. It's very easy to use, the workspace is very intuitive, plus you can request a specific illustration for the platform designers. It has also the biggest illustration library that I know.