Looking at that butt splice to the fusible link, I'll wager at 50% odds THAT is your original problem. Butt splices come in two quality levels: BAD and UTTERLY USELESS. I recommend you use a connector which will permit you to undo the connection if needs be AND gives an ELECTRICALLY and MECHANICALLY SECURE CONNECTION. I like 3M Scotchlock wirenuts or split brass bolts taped with rubber tape, then cloth friction tape. You can always solder the connection and use shrink-wrap also.
I had a starter relayt issue in 2018. Turned out the original factory crimped connection had burned down to the LAST STRAND OF WIRE. I could get it to start with a jump only because the absurd amount of current then would momentarily get through the single strand of wire to engage the relay.
I put a new connector on and the old relay has worked splendidly ever since. If you want to install a new one, get Standard/Blue Streak. There are few good brands anymore..... maybe try an NOS one if you can snag it.