Is the word soltei the same in Brazilian and European Portuguese?

Yes

There are no differences in meaning, grammar, or spelling for the word "soltei" between Brazilian and Continental Portuguese. It is the first-person singular preterite (past tense) of the verb soltar. The only difference lies in pronunciation: Brazilian Portuguese tends to have more open, clearly articulated vowels, whereas Continental Portuguese features significant vowel reduction, often making unstressed vowels sound much more closed or nearly inaudible.

Brazilian Portuguese

1. Soltei o cachorro no quintal. (I let the dog loose in the backyard.)
2. Soltei o nó do cadarço. (I loosened the shoelace knot.)
3. Soltei o freio de mão. (I released the handbrake.)
4. Soltei a verdade para ele. (I let the truth out to him.)
5. Soltei um grito de susto. (I let out a scream of fright.)

Continental Portuguese

1. Soltei o cão no quintal. (I let the dog loose in the backyard.)
2. Soltei o nó do atacador. (I loosened the shoelace knot.)
3. Soltei o travão de mão. (I released the handbrake.)
4. Soltei a verdade a ele. (I let the truth out to him.)
5. Soltei um grito de susto. (I let out a scream of fright.)