I have a '91 Volvo that won’t shift out of park in the mornings. The button on the shifter simply wont depress to allow it to move out of park. If you turn the car on and let it run for about 5-10 minutes it has no problem moving into drive or reverse.
This is likely a problem with the shift interlock switch. There is a safety mechanism that won’t allow you to shift out of park w/out your foot on the brake. Yours is sticking. Given that the button won’t push in, your problem is likely right there at the bottom of the shifter. If you pull your center trim console you’ll be able to see a little catch that is supposed to move out of the way. Its probably controlled by a little solenoid. That is probably gummed up from 20 years worth of spills & other gunk. Getting in there & cleaning it up will likely correct this.
If the problem isn’t there it may be at your brake light switch (look under the brake lever) which is what will tell the thing that its ok to move out of the way.