RepairPal Certified shops can diagnose and repair your 1997 Nissan Altima. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.
Could be a shift fork issue, synchros, etc. This would require a hands-on inspection by someone who works on manual transmissions.
Use this link to find a good shop near you.
https://repairpal.com/repair-shops
Alex