Poor audio levels, too high or too low, are not uncommon with video tapes, especially home made recordings.
A passive volume control can cut level, but not boost low level recordings, it offers no tone control capability, and would not support voice over and similar recordings efforts.
I find a low cost mixer to be very useful because it can boost and cut levels, adjust channel balance, and provide tone control. This is but one example of a large variety of mixers on the marker.
https://www.
amazon.com/Mackie-Mix-Mix8-8-Channel-Mixer/dp/B00ND1KGEI/ref=sr_1_8?dchild=1&keywords=mackie+mixer&qid=1604 500261&sr=8-8
Also, it is worth noting that there are a lot on the used market as well, and the audio mixers are not quite as likely to be trashed as VCRs due to many fewer moving/wearing parts and operating at audio frequencies. The main issue I've encountered is "scratchy" level controls - a squirt of something like CRC QD Electronics Cleaner can often help that.