Welcome to the forum.
No not a clutch issue.
Reads like one of the three shift forks has come loose inside the transmission.
Transmission will need to come out to fix it, most likely a 30 cent roll pin but you need to take off the top cover to fix it.
But do this first: TRS Magazine - Shifter Bushing Replacement
Pull off the shifter, look down inside and you will see 3 shift "slots"
2 "slots" seen in last picture in above link.
Those slots are pushed forward and backward to select the 6 gears
closest slot to driver is for 5th/reverse
center is for 3rd/4th
farthest is for 1st/2nd
When the slots are all lined up in the center that is Neutral
Those slots are attached to the shift rails, long bars, with a roll pin, then on each shift rail is a shift fork also attached to rail with a roll pin.
When you shift gears the shifter arm slides one slot forward or backward which moves the shift fork forward or backward which selects the gear.
Because of the way it is setup, the width of the slots and shifter arm, only 1 gear can be selected at a time.
Unless shifter fork breaks, happens but not often, or a roll pin falls out or is sheared off by forcing shifter arm into a gear, which is far more common.
But in any case the trans will most likely need to come out to access the top plate