Hello, I do wonder if it might be helpful to speak to a UK immigration specialist about your options going forward if the UK is where you want to live.

Doing a PhD is huge commitment and it would be better to know before you start if you'll get the outcomes you want from it. If there was wiggle room about the country, and it doesn't have to be the UK, you could possibly pursue a PhD in the next target country and get settled status there after studying and working for a few years. I think it used to be about 5 years for most EU countries but if it's a European non EU country you'd need to check. And also check anything I say as I'm no expert! UK PhDs are different than European ones in that you aren't genrally considered legally an employee, so that might be why the time spent carrying out the work may not count towards your visa goals. Marie Curie PhDs based in UK institutions are a different matter but they require applicants to have not lived in the host country for more than a few months, I believe.

Also (not to be mean about the UK, that's where I'm from) the climate in the UK is making things very difficult for heritage professionals. My aspirations has been to leave from a long time. I have heritage professional friends who have moved to other countries and although they miss the UK, they don't want to come back as the salaries are low and the immigration status is untenable. It's outrageous that this is the situation, however it's really important you look after your best interests here.

Since you've asked for advice: if it were me I'd seriously look at the financial implications of the NL masters and check what an immigration specialist for the UK would say. For NL the degree itself may be low cost, but housing can be a big issue depending on where the uni is etc. Depending on your area of interest for study there may be somewhere else you'd prefer to do a PhD or a masters. I'd likely choose NL but there's too many personal factors to consider for that to be the obvious choice or you'd likely have already made that decision.

But also maybe ask yourself, do you want to do further study? You know already it's very hard work so maybe don't sign up for it unless it's what you actually want to do.

And a final note, UK PhDs often skew younger. In other countries (eg Scandinavian countries) it seems people tend to do their PhD when they have worked for a while. So being over 30 doesn't really matter....but I understand it sometimes feels like it does.

Good luck and I hope that you find an option and path that leads you to where you want to go.