Permitted work from start of NS ESA claim

My client was working for over 1 year and then became ill and was on SSP from Nov 2021 He tried going back to work at reduced hours which was agreed with his pyschiatrist, then reduced hours further to 15 a week. He is currenlty off sick again, SSP has run out now, but he is still employed and he wants to go back to work,probably even less hours for a start. He has been on UC since the time his SSP had started. He does not get the HC element as he lives with his mother
I have not had any clients with permitted work for a long time, when there was still a 52 week limit on permitted work higher limit, but I think this is gone now.
Would he be now be able to claim NS ESA and do permitted work straight away, provided he stays within the earnings limit (and hours limit, unless the involvement of his MH Team can somehow make this supported permitted work)?
Thanks in advance for any help with that.