Repairing, of course, depends on the damage. If it's torn pages, success of a repair depends on the torn edge, whether it's laterally torn or cleanly with no offset.
Lateral tears could be glued [1], but clean tears will need some additional support, which could be non-trivial, if no-tape is preferred.
Well, for some books, tape-repair is not such a bad idea, esp. if it's in active, often "doomed-by-design", use (aka young kids). Well, could be a teaching moment on "healing the hurt book" and how not to hurt them any more.
Thick pages could be split-sliced too and then reinforced, if it's worth the hassle and a sharp blade hazard.
Reparing the joints could be also reasonably reinforced with matching paper and glue.
Fixing the broken spines may need disassembly and reattachment of the cover.
Broken stitching too will need cover disassembly and restitching of the damaged booklet. If the binding is not threaded but glued, then hopefully it could just be reglued. The trick is in salvaging the spine (if there's any title or design on it).
Book restoration is even harder, as you may be dealing with something of irreplaceable and high value. So consult the pros.
[1]: https://feltmagnet.com/crafts/how-to-repair-a-torn-page