Hey @kyanokashi, welcome to the community 
Could you try the type casting functionality integrated into n8n’s Postgres node and specify the update column like id:uuid instead of id (replace id with your actual column name)? This did the trick for me:
My test table had a structure of CREATE TABLE kyanokashi (id uuid DEFAULT uuid_generate_v4(), name VARCHAR);.
If the above doesn’t work for you, could you confirm how your table looks like and share the workflow you are using?