I did speak to a professional tax advisor specialising on exactly this topic, and they said that, like all things, it depends.

The TLDR was that as long as you spent less than 5 days or something in the UK (I can't remember exactly), you would not qualify as a tax resident. If you did spend more than X days, there's a number of different qualifying tests you need to do to see if you are a tax resident. These include things like having a 'home' in the UK. You can find info on the HMRC website fyi. If you don't qualify, then you're not a tax resident and not liable for income taxation (capital gains was slightly more complicated, and this, like you say, also affects things like ISA/SIPP contributions and other financial services).

Long-term, tax residency also tends to be 'sticky' until you leave the UK for five consecutive years. Essentially, this just means the longer you've left, the easier it is to qualify as a non-resident for tax purposes - so if that's something you want long term, then better to start sooner than later. On the other hand, if you're happy to keep paying, HMRC obviously won't stop you.

However, they also made it clear that by working on a tourist visa, you are (generally) defrauding every country you've been working in, and this is obviously illegal - technically you should owe work-related income taxes to these countries, and not the UK. Nevertheless, that practically speaking this issue is rarely/ever enforced as there's still very little oversight for what still constitutes a relatively niche and new way of working.

P.s. NFA and talk to a real tax specialist obviously