A lot of things you could do. Landscaping would be a good one. You would need to check local regulations. A lot of municipalities are now limiting hours any sort of outside construction can be done due to noise and disruption of neighborhoods. Stupid but is what it is.
Sprinkler system maintenance and care. Most of the landscaping and installation companies only like to put them in. They are easy to work on. Set up in spring to turn them on, tune the heads and make sure all the heads and valves are working. Program boxes for people. 90% of homeowners can't even set the program up. Repair and trouble shoot them in the summer. In the fall rent a commercial air compressor and blow them out, shut them down for the winter.
Handyman if you can do basic construction. Huge need and pays well. I had a hole in my ceiling from a small water leak. I don't do drywall. Hole was less than 1ft square. I couldn't find anyone that wanted to fix it. Finally tracked someone down, HIs work time at the house was about 3 hours total. Cost me $1300. Guys just name their price on small jobs because no one wants to do them. Wait times are generally weeks to months, if you can get a hold of someone.
Appliance repair is another good one. Being an engineer you should be able to step right into that. If you can run a multi meter and have a basic understanding of switches and circuits you are good to go. Our washer just broke. I usually fix it. Control board went bad for the second time in 3 years. I called to have it looked at to try to get Maytag, (don't buy a Maytag) to do something about it. Place where I bought it doesn't have any technicians, can't find any. Local repair place, 3 week wait just to get it looked at.
Mechanic work. If you are so inclined. Could just do basic stuff and stay busier than you wanted if you have tools and a place to do it. Small engine repair.