Did he take classes through a tutor or school? If so, see if the instructor will write a quick letter.
When the pandemic started and schools were closed down. I know a few people that used a letter and the canton asked for the certificate the next renewal.
Similarly N of 1, but evidence of attendance to language courses (copy of contract, register of attendance) plus commitment to submit certificate has also worked.
I renewed my B Permit in Baselstadt last June, all I had to do was let them take a photocopy of my passport at the immigration office and they sent me out an appointment. Everything was held up because of Covid and they told me not to worry if my existing permit expired.
The appointment consisted of having a digital photo and my fingerprints taken along with my signature. German A1 was never mentioned and everything at the appointment was handled in English. My new credit card style permit was with me within about 5 days.