According to The New York Times, the Trump Administration is not currently planning to invoke the 25th Amendment and make Pence Acting President. But let's suppose they did.
Currently, the Senate is split 53-47, which is rather close, and Martha McSally stands a fair chance of losing her seat in November (as an appointee, she is not entitled to sit out the lame duck session if she loses the race), which could bring that number down to 52-48. Additionally, two Republican senators (Lisa Murkowski and Susan Collins) will vote against confirming Amy Coney Barrett, so it's possible this vote will be deadlocked 50-50.
If Pence is Acting President, and the Senate deadlocks, can he still break the tie, or does the vote fail?
(It's fairly obvious that if Trump dies and Pence becomes the for real President, he would not be Vice President any more and could not break ties. So this is specifically about the title of Acting President.)