These require surface mount brackets that might be about as deep as the current fluorescent fixtures

https://www.e-conolight.com/c-tr-c-fp24-62l.html

https://www.lightingsupply.com/cree-c-tr-c-fp24-62l-35k-wh

https://www.superbrightleds.com/cat/led-panel-light/filter/LED_Color,Warm_White,137,4650:LED_Color,Selectable_CCT,137,20224:Product_Type,2x2_Panel_Light,263,17174:Product_Type,2x4_Panel_Light,263,17176:Product_Type,1x2_Panel_Light,263,17177:Product_Type,1x4_Panel_Light,263,17178:

https://www.superbrightleds.com/moreinfo/panel-light-mounting/2x4-surface-mount-kit-for-panels/4795/10391/

https://d114hh0cykhyb0.cloudfront.net/pdfs/LPD-TWR_Manual_V4.pdf