This 100%.
Just to give another viewpoint on this, having just started going full time on my solo agency, I actually love doing the sales and marketing stuff and scoping the work for clients. Yes, it does take a lot of time away from pure technical work but I do enjoy the balance of it. So, it does depend on your own interests and how you like to spend your time. Freelancing/Consulting is definitely not for everyone. And tbh, lets see maybe in a year or two I will be fed up of the sales/marketing stuff too.
One thing I will say though is that, it also comes with a lot of flexibility and freedom and you set our own hours and location which in itself is very valuable. Of course has its own pros and cons and you have to be quite disciplined to begin with.
The best is proof of work. If you don't have any, build something and show that off. Even listing out the companies you have worked for will be good. Cold email could work if its not completely "cold", i.e, find companies/people who are in the space/industry where you have worked so that they can see you have solved a similar problem before. 10+ years of software engineering is quite valuable, you just have to present yourself in a way where the value can be seen.
Also, never, ever work for free. One, your time is worth more than you think. Second, it makes you sound a bit less serious and less valuable and you will attract clients that are not fun to work with. Not worth your time at all. The only people who MAYBE should be working for free are students who are in high school.
I have been freelancing on and off on the side for the past 8 years and this year pulled the plug and going full time on it and tbh I am now oversubscribed. So, there's definitely a need for it.
My first few clients (8 years ago) were through posting on reddit (/r/forhire) and then also on the monthly HN freelancer thread (was shocked they stopped doing that, I have gotten 2 solid clients from those!).
One thing I will say though is that, it also comes with a lot of flexibility and freedom and you set our own hours and location which in itself is very valuable. Of course has its own pros and cons and you have to be quite disciplined to begin with.