Adding some from Scotland I have experience with and afaik take donations, some are broader but with good trans inclusion:
Scottish Trans - Trans advocacy, information and social events. Run by the Equality Network, a broader Scottish LGBTQI advocacy group.
LEAP Sports Scotland - Sports charity that advocates for queer inclusion in sports, runs trans sports groups (Trans Active) in at least Glasgow and Edinburgh that I can absolutely recommend.
LGBT Health & Wellbeing - Not trans specific but includes trans specific, trans led and trans inclusive support and social events, and supports a variety of smaller community-run subgroups.
And another couple UK-wide:
Gender Identity Research & Education Society - Trans led charity supporting research on trans matters and education/training on trans inclusion. Does consultancy for public and private sector organisations.
Trans Kids Deserve Better - Trans advocacy and activist group led by and for trans kids. They do good work.