Steps to reproduce:
1. Set the system region format to one whose decimal separator is a comma, for example Region: Germany with any language (System Settings > General > Language & Region)
2. Create a new project. The Editor reads the region format once at startup, so it has to be created after step 1
3. Import the attached A560Source.cs into Assets
4. Select Assets > Create > A560 Source. The new asset's Text field reads 1.5
5. Select Assets > Create > UI Toolkit > UI Document and open it in UI Builder. In the Library pane enable Editor Extension Authoring and drag a Float Field into the Hierarchy
6. With the Float Field selected, in the Inspector set Data Source to the A560 Source asset, then add a binding on its Value attribute with Data Source Path set to Text and Binding Mode set to To Target
7. Read the Float Field in the UI Builder canvas

Actual result: the Float Field displays 15. The source string is 1.5, and the conversion reports success while returning a value ten times too large.

source string        1.5
Float Field shows    15

The same round trip through the public binding API, with the culture taken only from the system region format and not set in code:

culture=en-DE
float 1.5    -> string '1.5'   written with the invariant culture
string '1.5' -> float 15       read with the current culture, returns true

Integral values round-trip correctly, so the failure is specific to the decimal separator. In a region format where the dot is neither the decimal nor the group separator, for example Region: France or Region: Lithuania, the value becomes 0 instead of 15, and the conversion still reports success. The same conversion is used in the other direction, so a Two Way binding on a Text Field redisplays a typed 1.5 as 15 and writes 15 back to the source.

Expected result: the Float Field displays 1.5, in every region format, or the conversion reports failure instead of returning a wrong value.

Reproducible with versions: 7000.0.0a5

Not reproducible with versions: 6000.3.24f1, 6000.5.5f1, 6000.6.3f1, 6000.7.0b2 (macOS only: before 7.0 the Editor reports en-US regardless of the system region format, so the region format cannot reach the conversion there. The same round trip does return 15 on those versions when the culture is set from code instead, so the defect is present and only the reachability differs. In 6000.0.0f1 the string to float conversion is not registered at all and the call returns false)

Tested on (OS): macOS 26.0, Apple silicon