What would be the best tag for searchung transgender characters? since alot of them are tagged as boys for example bridget

There's the "transgender" tag, however it has less than 300 results tied to it.
Here's the wiki page for it which has some related tags:
* gelbooru.com/index.php?pa...=&s=view&id=27374

You also have tags like "male_with_breasts" that might be helpful in finding transgender characters, but it mostly seems to be used for non-trans characters with breasts added.

We usually tag by physical features or "sex" instead of canon "gender".
It's more about tagging what you see, not what you know through context.

"trap" or "crossdressing_(mtf)"

I brought over these tag groups from Danbooru onto our wiki, they should help.
Not sure how many of these tags are actually used regularly though.

Transgender tag group:
gelbooru.com/index.php?page=wiki&s=view&id=32435

Gender non-conformity tag group:
gelbooru.com/index.php?page=wiki&s=view&id=32434

You all have NO idea how much I hate this dumbass tag. Especially when used on transgender characters.

for tagging reasons, it makes archiving and search really simple,

Trap = everyone is gay for Bridget
Futa = gal with dick
Newhalf= gal with dick and balls

done. no further complication for a fap session

If somebody who knows nothing about the character would instantly think the character is a girl unless told otherwise, then you use the "trap" tag.

Essentially it's for male characters who pretty much have a female character design.

Same deal for "reverse trap", but flipped the other way.

And honestly, alot of anime characters pretty much have the exact same face with a few tiny differences.
Both male and female characters a lot of the time.
The only thing really distinguishing them apart is hair, breasts, muscular body/frame, and clothing.
Otherwise male and female characters would be kinda hard to tell apart.

Take skinny male character, give them prettier hair, and put them in female clothing.
And suddenly they look exactly like a female character with small/flat breasts.
Hence, "trap".

Take a female character with small breasts, give them short/medium length hair, a male school uniform with a hoodie, and a bandaid or scuff mark on their face. All of a sudden they look like a teenage male character. A "reverse trap".

It becomes really subjective when you get into real life, like actual pictures/videos of people.