In a post from March, I wrote an overview of how an Indie author could increase the number of reviews s/he has. Most methods of getting reviews cost money, but joining a Goodreads group is one free method.
WARNING: There is at least one Goodreads Group that is solely marketing for a borderline scam outside site, Revvue. How Goodreads continues to allow this group to exist when every post by the moderators pretty much tells you to go to the Revvue website and use their service is beyond me. Avoid any Goodreads Group that solely exists to direct you to other websites. These violate Goodreads' terms of service. I suspect the moderators of this group are vigilant about making sure negative posts about Revvue are removed or are deflected.
I have been a member of many "review" groups on Goodreads since 2014. Some are good. Others have absent moderators, which causes them to turn into a spam board. I don't think you can even message moderators to draw their attention to issues anymore. The Reviewers, The Reviews Initiative for Indie Books, Genre Specific Review Groups, Christian Fiction Fans, GOOD REVIEWS, and Read 4 Review are all groups I've joined that no longer have active moderators. You can still join them (or at least most of them), but the rules that prevented people from spamming everyone are not necessarily being enforced. That means that you need to be extra careful if you want to use these--and you also should be aware that although desperate authors will join and post in any group, most readers who are real readers and not scammers tend to flee when the rules stop being enforced.
The groups below have somewhat strict spamming rules and do not just allow you to post your book and hope you get reviews. You must follow the rules, for example, some groups prohibit AI-generated work, and you must post any self-promotion in the appropriate threads.
The group I am most active in is Review Group. I joined this group in 2014 and, within this past year, joined the moderators of this group. Obviously, I am biased, but I feel we do a good job keeping the group focused and working together. Unlike many of the above-mentioned groups where you are posting and praying someone will see your book and review it, Review Group is primarily focused on review exchanges. There is a one-for-one list where members (who can be authors or readers) review a book on the list and, in exchange, can have a book they have written added to it. If they are just a reader, they can just state that when they post their review. There is also our standard rounds, where ten people join with one of their books. Each person reviews four people (who have never reviewed him/her) and gets four reviews for his/her book from people they have never reviewed. We are going to be experimenting with this format and reducing the number of reviews and the number of people in each group soon to see if it will be easier to fill groups. A lot of time and mental work go into creating these groups, and as they fill, it becomes more difficult to fit people into the group if they are not newer participants.
Similar to Review Group, I am in the Review / Write / Read Club (Indie & Self-Published) group. I am only a member of this group, but this group shares members/moderators with Review Group, so it operates on a similar basis. There is a one-to-one reading list that works like the one above. There are also "rounds" which are small 3-5 person versions of the 10-person rounds mentioned above, but you only get one review and give one review regardless of round size. Although moderating is still time intensive, these rounds are easier to form and fill because you are only looking for a conflict with two people. (You have to keep eight people from conflicting with each member of the ten-person rounds.) Unique to this group is also the "Chain." This is a group where you only have to make sure you don't have a conflict with the person above you in the chain. All of these groups are basically give a review to one person and get a review from someone else format.
The other group that I haven't participated in much, but it is actively moderated, is Readers Sharing Reviews. This group connects readers to free or low-cost books. It allows authors to self-promote their books as long as they follow the rules. There is usually a newsletter that gets delivered to your message box and highlights a few books. There are also occasional polls. This is a post-and-pray group, but it seems to actually have active readers instead of just authors trying to sell their books.