i think you should be able to import a .stl into most CAD programs, as one of that platforms native part files and save it as that. then you should be able to export that native part file to a step file.

Method 1: Using CAD Software (e.g., FreeCAD, Fusion 360)
FreeCAD (Free and Open-Source):

Download and install FreeCAD (available at https://www.freecadweb.org/).
Open FreeCAD and create a new project.
Import the STL file into FreeCAD:
Go to File > Open and select the STL file you want to convert.
Convert the mesh to a solid:
Select the imported mesh object.
Go to the "Part" workbench and click on "Create shape from mesh" to convert the mesh into a shape.
Then use the "Convert to solid" function under the Part menu to turn the shape into a solid object.
Export the object to STEP:
After the object is solid, go to File > Export, and choose STEP format (.step or .stp).
Fusion 360 (Free for hobbyists):

Open Fusion 360 and create a new design.
Import the STL file:
Go to the "Insert" menu and choose "Insert Mesh" to bring the STL file into Fusion 360.
Convert the mesh to a BRep (Boundary Representation) body:
Right-click the imported mesh and select "Convert to BRep".
After the conversion, the object becomes a solid model, and you can export it as a STEP file.
To export, go to File > Export, and choose STEP (.step) as the file format.
Method 2: Using Online Tools
Some online tools allow you to convert STL files to STEP files directly without installing software.

AnyCAD Exchange3D:

Visit AnyCAD Exchange3D.
Upload your STL file.
Convert the file to STEP format directly from the website.
Download the STEP file after conversion.
CloudConvert:

Visit CloudConvert.
Upload your STL file.
Choose STEP as the output format.
Start the conversion and download the result once it’s done.
Method 3: Using MeshLab + CAD Software
You can use MeshLab to clean the STL model and then import it into a CAD program for conversion to STEP.

MeshLab:
Open MeshLab and load the STL file.
Use the filters in MeshLab to clean the mesh (e.g., remove noise, simplify, etc.).
Export the model as an intermediate format (like OBJ or IGES).
CAD Software:
Import the OBJ or IGES file into FreeCAD or Fusion 360 and follow the steps above to convert it into a solid and then export as STEP.
Summary:
FreeCAD and Fusion 360 are excellent tools for converting STL to STEP because they offer precise control over the conversion process.
Online tools like AnyCAD Exchange3D and CloudConvert are useful for quick conversions, but may not handle complex geometries as effectively as dedicated CAD software.