I’ll do my best
Non-exec director is basically someone who doesn’t do the work (non-execution) but has a legal responsibility for oversight of the business.

A non-exec will usually sit on a monthly board meeting, listen, give advice, make introductions, and help ‘direct’ the business.
These can be paid positions or done as a vesting equity stake (1-3% ish?) or a mixture of both.
These either come through relationships with VCs and investors who trust you and know you are looking so will aim to put you in position to help with businesses they are investing in, or through being a known part of the eco-system through involvement in mentoring, advising, being employed, exiting, or investing for example.
These roles are also often advertised you can find them on linkedin.

EIR- Entrepreneur in Residence is generally someone experienced in startups who is attached to an accellerator/venture studio/incubator. They tend to have weekly short meetings with each team to track progress and give advice or act as a sounding board and are part of the long term relationship with a company during a programme to help those that run it, as opposed to mentors who tend to be one off meetings to give advice on specific topics at specific times.
You get these usually by being a mentor on a programme, or having been through a programme and becoming part of the system. These can sometimes lead to non-exec roles in companies that you add benefit to, or investment opportunities as you get early access to teams and know their trajectory. This is usually a paid position for the length of a cohort or project

Mentoring is like the above but less involved, this if not always a paid position as it is drop in mentoring and scheduling occasional calls and meetings with teams on programmes. This can often lead to running specific workshops (paid) and better relationships with organisers if you are seen to add value, which then can lead to EIR roles.

All of the above can generally be done part time around other work, it keeps you in contact with the eco system and allows you to spot opportunities in companies you would like to either join as an employee, co founder or investor.

It generally starts with identifying the local ecosystem organisers, getting to know them and letting them know you are looking for opportunities.

I have had all of the above roles after having co-founded multiple businesses to varying degrees of success and am now Programme Manager on an accelerator that I took my 2nd business on 10 years ago.

Happy to answer further questions

You sounds like you could add a lot of value to start-ups in a non-exec role. Sitting on a board and offering guidance.

There’s roles like ‘entrepreneur in residence’ and mentors in accelerators you might enjoy and could be done around other commitments.

It sounds like you are very good at your job, but situationally things have not been ideal

Launch now, but bear in mind there is no such thing as ‘build it and they will come’

Also bear in mind that cheaper does not mean you will make sales. Cheaper can mean untrustworthy, cheaper can mean you don’t value their problem. Price is a function of marketing rather than sales as they are not inversely proportional.